Dissociative photoionization of N 2 O in the region of the N 2 O + (C 2 Σ + ) state,studied by ion–electron velocity vector correlationM. Lebech, J. C. Houver, D. Dowek, and R. R. Lucchese Citation: The Journal of Chemical Physics 117, 9248 (2002); doi: 10.1063/1.1515765 View online: http://dx.doi.org/10.1063/1.1515765 View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/117/20?ver=pdfcov Published by the AIP Publishing Articles you may be interested in The role of Rydberg states in photoionization of NO2 and (NO+, O−) ion pair formation induced by one VUVphoton J. Chem. Phys. 139, 044311 (2013); 10.1063/1.4811713 NO+ formation pathways in dissociation of N2O+ ions at the C2Σ+ state revealed from thresholdphotoelectron–photoion coincidence velocity imaging J. Chem. Phys. 134, 054312 (2011); 10.1063/1.3549130 Dissociative photoionization of N 2 O in the region of the N 2 O + (B 2 Π) state studied by ion–electron velocityvector correlation J. Chem. Phys. 120, 8226 (2004); 10.1063/1.1651087 Vector correlations in dissociative photoionization of O 2 in the 20–28 eV range. II. Polar and azimuthaldependence of the molecular frame photoelectron angular distribution J. Chem. Phys. 117, 8368 (2002); 10.1063/1.1512650 Ion–electron velocity vector correlations in dissociative photoionization of simple molecules using electrostaticlenses Rev. Sci. Instrum. 73, 1866 (2002); 10.1063/1.1458063

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Dissociative photoionization of N 2O in the region of the N 2O¿„C 2S¿

… state,studied by ion–electron velocity vector correlation

M. Lebech,a) J. C. Houver, and D. DowekLaboratoire des Collisions Atomiques et Mole´culaires (L.C.A.M., UMR Universite´ Paris Sud et CNRS,No. 8625), Baˆtiment 351, Universite´ Paris Sud, F-91405 Orsay Cedex, France

R. R. LuccheseDepartment of Chemistry, Texas A&M University, College Station, Texas 77843-3255

~Received 20 May 2002; accepted 29 August 2002!

Imaging and time-of-flight-resolved coincidence techniques are combined to extend the(VA¿ ,Ve,P) vector correlation method to the study of dissociative photoionization of smallpolyatomic molecules breaking into two heavy fragments. Dissociative photoionization~DPI! of theN2O linear molecule into the N2O1(C 2S1) ionic state, induced by linearly polarized synchrotronradiation ~P!, is chosen as an example. The ion–electron kinetic energy correlation enables theidentification of all the DPI processes producing the NO1, N1, N2

1 , and O1 fragments. TheI xA¿(ue ,fe) molecular frame photoelectron angular distributions~MFPADs!, deduced from thespatial analysis of the (VNO¿/N¿ ,Ve,P) vector correlations, exhibit remarkable features. When theN2O molecule is aligned parallel to the polarization axis, a preferred electron emission from theN2O1 molecular ion in the direction perpendicular to the molecular axis, as well as a strongforward–backward asymmetry that favors electron emission along the molecular axis in the samedirection as the N1 or N fragment, are demonstrated. The measured MFPADs are found in goodagreement with the reported multichannel Schwinger configuration interaction calculations, whenmolecular rotation prior to dissociation is taken into account. This comparison provides anestimation of the lifetime of the N2O1(C 2S1) state prior to dissociation into the dominant channels@NO1(X 1S1)1N(2P)# and @N1(3P)1NO(X 2P)#, which is found to be about 2 ps. ©2002American Institute of Physics.@DOI: 10.1063/1.1515765#

I. INTRODUCTION

Measuring molecular frame photoelectron angular distri-butions~MFPADs! is a powerful means to gain informationon molecular photoionization dynamics.1 In this paper weaddress the determination of the MFPADs relative to a spe-cific molecular bond inside a small polyatomic molecule. Forthis purpose, an interesting opportunity is provided when dis-sociative photoionization~DPI! of a molecule takes place inthe frame of the axial recoil approximation,2 i.e., when thedissociation characteristic time is short with respect to that ofrotation. Then the orientation of the fragmenting molecularaxis can be inferred from the ion fragment recoil velocityvector, and the MFPADs can be determined in ion–electronvelocity vector correlation experiments. Qualitative informa-tion about the electron emission pattern in the molecularframe of small polyatomic molecules was first inferred fromthe shape of the ion fragment time of flight spectra byphotoelectron–photoion coincidence~PEPICO! spectros-copy.3,4 The first quantitativeI (ue) MFPADs for the valenceshell ionization of a polyatomic molecule were obtained byDownie and Powis,5 who studied the breaking of the C–Imolecular bond in CF3I excited by the 21.2 eV He radiation,using an angle-resolving photoelectron–photoion coinci-dence imaging technique. A comparable study of CH3Cl and

CH3F photoionization has recently been performed using thevelocity imaging coincidence technique.6 The quantitativeanalysis of theI (ue) MFPADs was also addressed in inner-shell photoionization of oriented polyatomic molecules likeCO2,7 probing the continuum wave functions of thesg* andsu* shape resonances. The experimental determination of theMFPADs has recently been combined with the use of ul-trafast laser technology, which enables time-resolved mo-lecular frame photoelectron spectroscopy,8 as illustrated bythe first dissociative multiphoton ionization~DMI ! study ofNO2 reported by Davieset al.9 Finally, in particular, forlarger polyatomic systems for which the requirement ofprompt dissociation with respect to molecular rotation maynot be satisfied, an alternative approach to the determinationof the MFPADs is to measure the laboratory frame photo-electron angular distributions for an ensemble of moleculesaligned or oriented by laser-induced optical pumping.10

In this paper we extend the velocity vector correlationapproach11 that we developed for the investigation of disso-ciative photoionization of diatomic molecules to the study ofDPI of simple polyatomic molecules following inner-valenceshell excitation, induced by linearly polarized synchrotronradiation~P!. For the simplest case of linear triatomic mol-eculesABC, like N2O, breaking into two heavy fragmentsand one electron (A11BC1e) or (AB11C1e), the(VA¿/AB¿ ,Ve,P) vector correlation method applies directly:it consists in measuring for each fragmentation event thea!Electronic mail: mogens@lcam.u-psud.fr

JOURNAL OF CHEMICAL PHYSICS VOLUME 117, NUMBER 20 22 NOVEMBER 2002

92480021-9606/2002/117(20)/9248/10/$19.00 © 2002 American Institute of Physics

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VA¿/AB¿ and Ve velocity vectors by combining time-of-flight-resolved ion–electron coincidence detection and imag-ing techniques. For simplicity, we use the indexA1 to rep-resent eitherA1 or AB1 in the following discussion.

The analysis of the (VA¿ ,Ve,P) vector correlation fol-lows the procedure established for the investigation of theDPI of diatomic molecules.11–13 The magnitudes of the ve-locity vectors provide the ionEA1 and electronEe kineticenergy correlation diagram~KECD! that identifies the stepsof the reaction pathway for each DPI process, in terms of theenergy position of the ionic or neutral intermediate state andthe dissociation limit. The resolution of the different pro-cesses in the KECD enables us to determine their branchingratios. Analyzing the directions of the velocity vectors, thecomplete angular distributionI (xA¿ ,ue ,fe) is obtained foreach process, wherexA¿ is the polar angle ofVA¿ referredto as then axis parallel to the linear polarizationP, ue is thepolar angle ofVe relative toVA¿ , andfe measures theVeazimuthal angle about the vectorVA¿ where then2VA¿

(n"VA¿) axis defines the direction in whichfe50. Whenthe axial recoil approximation2 holds, the direction ofVA¿

coincides with the breaking molecular bond axism at thetime of photon absorption, and (ue ,fe) are the electron po-lar and azimuthal emission angles in the molecular framedefined with thez and x axes alongm and n2m(n"m),respectively. Then theIxA¿(ue ,fe) molecular frame photo-electron angular distribution is obtained for anyxA¿ selectedorientation of the molecule with respect to the polarizationP.

Among the new aspects to be considered for triatomicmolecules with respect to the DPI of diatomic molecules arethat ~i! the neutral~BC! or ionic (AB1) molecular fragmentis usually formed in a distribution of vibrationally and/orrotationally excited states, which implies for each electronicstate a series of dissociation limits corresponding to the in-ternal states of the molecular fragment;~ii ! the relevant ionstate potential surfaces may lead to significant rotational ex-citation implying a more complex interpretation of the angu-lar information if either the predissociative or the dissocia-tive state has a nonlinear geometry;~iii ! for a linearpolyatomic molecule with electronic orbital angular momen-tum about the internuclear axisLÞ0 the rovibrational andelectron orbital angular momenta may interact giving rise toRenner–Teller effects.14

In this paper we report the results of the (VA¿ ,Ve,P)vector correlation study of the DPI of the N2O linear mol-ecule in the 20–22.5 eV photon energy range, where disso-ciative ionization produces two heavy fragments and oneelectron. We focus on the reactions involving photoioniza-tion into the N2O1(C 2S1) state, which corresponds to a 6shole in the (5s)2(6s)2(1p)4(7s)2(2p)4 valence electronicconfiguration of the N2O(X 1S1) ground state.15 This re-gion, where the ionization of inner valence electrons takesplace, is characterized by electronic correlation effects:16,17

satellite lines have been predicted16 and observed in photo-electron spectroscopy18 ~PES! and binary (e,2e) momentumspectroscopy.19 It lies a few eV below thes shape reso-nances identified in angle-resolved PES.20 MFPADs calcula-tions for photoionization into the N2O1(C 2S1) state usingthe multichannel Schwinger configuration interaction

method21 ~MCSCI! are presented and compared with the ex-perimental results. The same level of information for DPIprocesses involving photoionization into the N2O1(B 2P)valence state and higher inner-valence excited states, as wellas probing the influence of autoionizing states,22 will be re-ported in a forthcoming publication. The vibrational structureof the N2O1(C 2S1) state analyzed in high resolution PES23

is dominated by the~0, 0, 0! level and shows the weak ex-citation of the~1, 0, 0! and ~0, 0, 1! vibration modes. Theappearance of the~0, 1, 0! and~0, 2, 0! bending bands23 maypoint to a small deviation from linearity. Although no visibleline broadening was observed in photoelectron spectroscopy,a fast predissociation has been invoked for this state,24 whichwas shown to be completely predissociated into NO1, N21,N1, and O1 by photoionization mass spectroscopy.24

The ion–electron kinetic energy correlation diagram re-ported for each ionic fragment produced by the DPI of N2Ovia the N2O1(C 2S1) state, in which the~0, 0, 0! and~0, 0,1! vibrational levels are resolved, identify unambig-uously the dissociation limits, and provide their branchingratios. These results are compared with the previous ex-perimental results obtained by photoionization massspectrometry,24,25 threshold photoelectron–photoion coinci-dence ~TPEPICO!,26 and PEPICO4 spectroscopy. For theDPI processes producing the NO1 and N1 ion fragments, acomplete angular analysis is reported, providing the first de-termination of theIxA¿(ue ,fe) MFPADs for the N–NObreaking chemical bond, for any orientationx of the N–NOmolecular axis with respect to the polarization axis of theexciting light ~P!. They are obtained using the general formof the I (xA¿ ,ue ,fe) distribution derived for linear mol-ecules ionized by linearly polarized light,13 where the com-plete information is carried by the fourF00(ue), F20(ue),F21(ue), andF22(ue) functions involved in the expansion:

I ~xA1 ,ue ,fe!5F00~ue!1F20~ue!P20~cosxA1!

1F21~ue!P21~cosxA1!cos~fe!

1F22~ue!P22~cosxA1!cos~2fe!. ~1!

We note that for the studied N2O(X 1S1)→N2O1(C 2S1) photoionization transition, the determina-tion of the fourFLN(ue) functions allows the extraction ofthe magnitudes and phases of the dipole matrix elements, asdiscussed in Ref. 13. However, such a presentation of theexperimental data is omitted here to avoid lengthy develop-ments. The present results reveal strong electron emissionanisotropies in the molecular frame, which have not beenreported in previous studies. A comparison with the MCSCIcalculations allows us to estimate the predissociation lifetimeof the N2O1(C 2S1) state, as discussed in Sec. V.

II. EXPERIMENT

The velocity spectrometer equipped with two positionsensitive detectors~PSD! combines time-of-flight-resolvedion–electron coincidence detection and imaging techniques.It has been described in detail previously.11,12 Briefly, asschematically indicated in Fig. 1, the pulsed light beam~linesSA63 or SU5 at Super-ACO, Orsay! operated in the two-

9249J. Chem. Phys., Vol. 117, No. 20, 22 November 2002 Dissociative photoionization of N2O

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bunch mode crosses at a right angle the supersonic molecularbeam of N2O delivered by the SAPHIRS setup,27 definingthe interaction region. The rotational temperature of the mo-lecular beam is estimated to be about 35 K. TheP linearpolarization axis is parallel to the molecular beam. Ions andelectrons are extracted from the interaction region by meansof a dc uniform electric fieldE, whose magnitude~a few tensof V/cm! is chosen in order to ensure a 4p collection of bothcharged particles, ions and electrons, for the processes understudy. For each DPI event and each photon energy, the timeof flight ~TOF! and position of both the ion and electron arerecorded; thus, the three components of the ionVA¿ andelectronVe initial velocity vectors are determined.11 For thisstudy we have used a new development of the velocity spec-trometer involving two electrostatic lens sets (L1 and Le)outside the extraction region, which control the ion and elec-tron trajectories leading to an improved resolution in the de-

termination of the three velocity vector components.28 De-pending on the relative kinetic energy of the ion and electronfragmentsL1 , Le , or both lens sets are used. In the follow-ing we define the standard settings of each electrostatic lensby (VG15U;VE1520/93U;VE250;VT55/93U), whereVG15U, VE1, VE2, andVT are the voltages applied on theG1 final electrode of the extraction region, and theE1 , E2 ,andT electrodes that produce the nonuniform focusing elec-trostatic field.28

III. KINETIC ENERGY CORRELATION DIAGRAMS

The (EA1 ,Ee) KECDs shown in Figs. 2~a!–2~d! repre-sent the bidimensional histograms of the (A1,e) events thatresult from the analysis of the (VA¿ ,Ve) velocity vectors foreach of the four NO1, N1, N2

1 , and O1 ionic fragmentsproduced by the DPI of the N2O molecule, for a photonexcitation energyhn521.2 eV. A process appears in such adiagram as an accumulation of data points forming a peak ora ridge, characterized by the set of kinetic energies of the ionand electron (EA1 ,Ee). The (EA1 ,Ee) representation is pre-ferred here to the alternative possibility of plotting the dis-tribution of events as a function of the center-of-mass kineticenergy release of the two heavy fragments~KER! and theelectron energy, because it enables a direct evaluation of theactual kinetic energy of each ionic fragment: The (EA1 ,Ee)presentation is then more informative from the perspective ofthe subsequent angular analysis which requires a sufficientkinetic energy of both the ionic fragment and the electron.The 55 V/cm extraction field chosen for this experiment,combined with the use of theLe electron trajectory focusinglens in the standard setting, ensures a 4p collection of ionsand electrons in the particle kinetic energy range (EA1

<1.5 eV andEe<4 eV). This range corresponds, in particu-lar, to the DPI processes involving photoionization into theN2O1(C 2S1) state, dominated by the~0, 0, 0! vibrationallevel (Ee51.09 eV) and the N2O1(B 2P) state (2 eV<Ee

<3.7 eV), or into other ionic states lying in this region. Forthis extraction field the ion TOF spectra enable a proper massseparation of all the ionic species, in particular, the backward~BW! NO1 ions emitted in the direction opposite to the ex-traction field are separated from the forward~FW! N2

1 ionsemitted in the direction of the extraction field. Figure 2 is aclear illustration that predissociation of theB 2P state prin-

FIG. 1. Scheme of the electron–ion velocity spectrometer~for details seeRefs. 12 and 28!.

FIG. 2. KECDs of the~a! (NO1,e), ~b! (N1,e), ~c! (N21 ,e), and ~d! (O1,e) events identifying the DPI processes of N2O at hn521.2 eV, using an

extraction field of 55 V/cm combined with theLe standard focusing lens set. The straight linesLD,vA1 indicate the dissociation limits~see Table I!. The intensity

scale runs from blank~lowest intensity! to black ~highest intensity! in linear scale, for each KECD; the contour lines are spaced by 10% of the maximumvalue.

9250 J. Chem. Phys., Vol. 117, No. 20, 22 November 2002 Lebech et al.

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cipally leads to NO1 and N21 ionic fragments, whereas pre-

dissociation of theC 2S1 state produces the four NO1, N1,N2

1 , and O1 ionic species. It provides a global view of allthe DPI processes, as well as the determination of theirbranching ratios.

Energy and momentum conservation impose for each(A1,e) DPI process, leading to final products (A11B1e), the @Ee1(11MA /MB)3EA15hn2ED# linear rela-tionship between the kinetic energiesEA1 and Ee of thefragments, whereED is the potential energy associated withthe dissociation limit of the reaction,hn the excitation en-ergy, @(11MA /MB)3EA1# the kinetic energy released bythe dissociation. We label asLD,v

A1 the straight line that cor-responds to the production of theA1 ion, where the indexDnumbers the dissociation limit starting from the lowest one(D51) andv labels the vibrational level of the molecularfragmentA or B when specified. Accordingly, the straightlines of slope222/7,222/15,211/4, and211/7, which cor-respond to the main relevant dissociation limits labeledLNO1, LN1, LN21, andLO1, respectively~see Table I!, aredisplayed in each bidimensional histogram. Each peak corre-sponding to an identified process shows up on one of thesestraight lines, attesting which of the dissociation limits arepopulated. A set ofED(v,J) values characterizes a series ofdissociation limits of a given electronic energy, correspond-ing to the vibrational and/or rotational internal states of themolecular fragment. In the following we consider only thevibrational distribution, since different rotational states of themolecular fragments cannot be resolved.

For photoionization into theC 2S1 state, the character-

istics of the energy distributions and the identification of thedissociation limits for each ionic species can be extractedfrom Fig. 2, with the use of Table I. They are consistent withthe results of the PEPICO experiment of Kinmondet al.4

at hn521.2 eV. The dominant reactions correspond tothe following dissociation limits: @NO1(X 1S1,v53)1N(2P)# (L3,3

NO1), @NO(X 2P,v51,2)1N1(3P)# (L1,122N1 ),

@N21(X 2Sg

1 ,v51,2)1O(1D)#(L3,2N21), and @N2(X 1Sg

1 ,v54,5)1O1(2D)# (L2,425

O1 ). The measured branching ratiosbetween the ionic species for DPI via theC state determinedby integration of the peaks in the KECD are as follows:BR(NO1)'74%, BR(N1)'11%, BR(N2

1)'11%, BR(O1)'4%, in very good agreement with the results of Kinmondet al.,4 and consistent with earlier results.24,26

Figure 3 displays a detailed view of the KECDs for the(NO1,e) ~a! and (N1,e) ~b! coincident events that corre-spond to the breaking of the N–N bond induced by dissocia-tive photoionization via theC 2S1 state, for a photon exci-tation energyhn520.54 eV. There, an extraction field of 12V/cm combined with the use of theL1 and Le trajectoryfocusing lenses for ions and electrons that ensures a com-plete collection of the charged fragments, enable us to im-prove the energy resolution and resolve vibrational struc-tures. The~0, 0, 0!, ~1, 0, 0!, and~0, 0, 1! vibrational levelsof the C state, which correspond to the (Ee'0.43, 0.276,0.147 eV! electron energies, respectively, are partially re-solved in the two (NO1,e) and (N1,e) KECDs, whereDEe'150 meV. Their relative intensities of about~75%,10%, 15%!, obtained from a complementary analysis, areconsistent with that measured by photoelectronspectroscopy23 when all the fragment ions are considered.For the selected N1 fragment, a~85%, 5%, 10%! slightlydifferent distribution is found. In the (N1,e) KECD, the(v50, 1, 2) vibrational distribution of the NO(X 2P) mo-lecular state (DEv'230 meV) in the @NO(X 2P,v)1N1(3P)# (L1,v

N1) outgoing channel after predissociation ofthe C(0, 0, 0) level, which corresponds to aDEN1 energyspacing of 157 meV, is completely resolved. Figure 3~c! pre-sents a fit of theEN1 distribution: the relative intensity of thethree (v50, 1, 2) vibrational levels is~25%, 40%, 35%!.The maxima of the peaks is shifted by about 30 meV withrespect to the position for the lowest rotational level. Thelower panel of the (N1,e) KECD indicates a (v50, 1, 2, 3) similar tentatively resolved structure after pre-dissociation of theC(0, 0, 1) level, in the limit of the statis-tics, with an intensity distribution that favors now the (v50, 1) levels of NO(X 2P). The measured vibrational dis-tribution of the NO~X! fragment is consistent with that in-ferred from the PEPICO4 and TPEPICO26 spectra. On theother hand, the elongated major structure in the (NO1,e)KECD @Fig. 3~a!#, which peaks on the@NO1(X 1S1,v53)1N(2P)# (L3,3

NO1) after predissociation of theC(0, 0, 0)level, is not vibrationally resolved. Resolving theNO1(X 1S1,v) distribution (DEv'280 meV) would corre-spond to aDENO1 energy spacing of about 90 meV, justbelow the 100 meV ion fragment energy resolution in thepresent experimental conditions. The envelope of theNO1(X 1S1,v) vibrational distribution extends fromv50to v56, consistent with the results of Kinmondet al.,4 and

TABLE I. Dissociation limitsLD,vA1 for N2O1 and their potential energies

ED . LDA1 is LD,v

A1 with v50. The limits corresponding to the dominant peaksobserved in the KECDs in Figs. 2 and 3 are in bold character.

Dissociation limitLDA1 ED ~eV! Products of dissociation

12.89 X 2PL1

NO1 14.19 NO1(X 1S1)1N(4S)L1

O1 15.29 N2(X 1Sg1)1O1(4S)

16.38 A 2S1

L2NO1 16.57 NO1(X 1S1)1N(2D)

L1N21 17.25 N2

1(X 2Sg1)1O(3P)

17.65 B 2PL3

NO1 17.77 NO1(X 1S1)1N(2P)L3,3

NO¿ 18.63 NO¿„X 1S¿, vÄ3…¿N„

2P…

L2N21 18.39 N2

1(A 2Pu)1O(3P)

L2O1 18.61 N2(X 1Sg

1)1O1(2D)

L2,4O¿ 19.75 N2„X

1Sg¿ , vÄ4…¿O¿

„

2D…

L2,5O¿ 20.02 N2„X

1Sg¿ , vÄ5…¿O¿

„

2D…

L3N21 19.22 N2

1(X 2Sg1)1O(1D)

L3,2N21 19.76 N2

¿„X 2Sg

¿ , vÄ2…¿O„

1D…

L1N1 19.46 NO(X 2P)1N1(3P)

L1,1N¿ 19.69 NO„X 2P, vÄ1…¿N¿

„

3P…L1,2

N¿ 19.93 NO„X 2P, vÄ2…¿N¿„

3P…20.11 C 2S1

L3O1 20.31 N2(X 1Sg

1)1O1(2P)

L4N21 20.34 N2

1(A 2Pu)1O(1D)

L5N21 20.48 N2

1(B 2Su1)1O(3P)

L4NO1 20.60 NO1(a 3S1)1N(4S)

L2N1 21.36 NO(X 2P)1N1(1D)

9251J. Chem. Phys., Vol. 117, No. 20, 22 November 2002 Dissociative photoionization of N2O

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indicates that the@NO1(X 1S1)1N(2D)# (L2,324NO1 ) disso-

ciation limit contributes to theENO1 high-energy tail. Thepopulation of the two (L2

NO1) and (L3NO1) dissociation lim-

its, preferably on thev54 level, appears unambiguously inthe identification of the minor processes associated with thepredissociation of theC(0,0,1) level in the lower panel ofthe (NO1,e) KECD.

IV. MOLECULAR FRAME PHOTOELECTRONANGULAR DISTRIBUTIONS

In this section, the spatial analysis of the (VA¿ ,Ve,P)vector correlation is presented for the two major processesthat correspond to the breaking of the N–N molecular bondfollowing photoionization into the N2O1(C) state, identifiedin the KECDs discussed above:

N2O~X 1S1!1hn→N2O1„C 2S1~0,0,0!…1e

→NO1~X 1S1!1N~2P!1e, ~2!

N2O~X 1S1!1hn→N2O1„C 2S1~0,0,0!…1e

→N1~3P!1NO~X 2P!1e. ~3!

The complete angular distributionsI (xA1 ,ue ,fe) are pre-sented according to the general analytical form given in Eq.~1!. As discussed previously for the DPI of diatomicmolecules,13 the best statistical determination of theFLN(ue)functions is obtained after a Fourier analysis infe of the

I @xA1#(ue ,fe) functions for the four molecular axis orienta-

tion selections: 0,xA1,180°, 0,xA1,90°, 90,xA1

,180°, and 60,xA1,120°.The measuredFLN(ue) are displayed in Figs. 4~a! and

4~b! for the processes, Eq.~2! and Eq.~3!, respectively, anda photon excitation energyhn520.9 eV. This experimentwas performed with an extraction field of 16 V/cm, com-bined with the focusing lens standard settings for electronsand ions. TheFLN

NO1(ue) and FLNN1(ue) exhibit significant

anisotropies, and a striking mirrorlike angular dependence,symmetric with respect toue590°. TheF00(ue) andF20(ue)functions present a first maximum forue590°, and a secondmaximum forue5180° (NO1) or ue50° (N1). This be-havior reflects a significant molecular frame forward–backward~MF–FW–BW! asymmetry, which favors electronemission along the molecular axis in the direction of the Nfragment. TheF21 function, which characterizes the cos(fe)azimuthal dependence of the MFPAD for an orientation ofthe molecular axis at the magic angle with respect to thepolarization axis, displays a strong oscillatory variation, witha single structure in the 0<ue<90° range and a doublestructure in the 90<ue<180° range for the NO1 ionic frag-ment, and the opposite with a reversed sign for the N1 ionicfragment. TheF22 function, which characterizes the cos(2fe)azimuthal dependence of the MFPAD for the molecular axisoriented perpendicular and at the magic angle with respect tothe polarization axis, is negative in the 0<ue<120° domain

FIG. 3. DPI processes of N2O observed in the KECDs of~a! the (NO1,e) and~b! the (N1,e) events athn520.5 eV, using an extraction field of 12 V/cmcombined with theL1 andLe standard focusing lens sets. The straight linesLD,v

A1 indicate the relevant dissociation limits for these processes~see the text!.The intensity scale runs from blank~lowest intensity! to black~highest intensity! in linear scale, for each KECD; the contour lines are spaced by 10%~a! and8.3% ~b! of the maximum value; the scale of the low electron energy (Ee,0.22 eV) panel is amplified with a factor of 4 in~a! and a factor of 3 in~b!. ~c!N1 kinetic energy distribution after predissociation of theC(0, 0, 0) level~integration over electron energies: 0.3<Ee<0.55 eV) fitted by a sum of threeLorentz functions. The expected kinetic energies of the N1(3P) fragment corresponding to the population of the NO(X 2P;v50,1,2;J50) levels are marked.

FIG. 4. FNL(ue) functions (—d—F00 ,—m—F20 ,—j—F21 ,—s—F22) for the DPI processes definedin Eq. ~2! ~a! and Eq. ~3! ~b!, measured athn520.9 eV, using an extraction field of 16 V/cm com-bined with theL1 andLe standard focusing lens sets.

9252 J. Chem. Phys., Vol. 117, No. 20, 22 November 2002 Lebech et al.

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for the NO1 ionic fragment, then becomes approximatelyzero before finally becoming slightly positive at aboutue

'135°, and its variation is symmetric with respect toue

590° for the N1 ionic fragment case. The observed behav-ior of the FLN

NO1(ue) and FLNN1(ue) functions shows that the

electron is emitted from the N2O molecule ionized into theN2O1(C) state prior to dissociation: the electron emissiondistribution with respect to the N–N molecular axis and thepolarization axis is then identical whether the NO1 or theN1 ionic fragment is formed, taking into account the (ue

N1

→p2ueNO1 ,fe

N1→p2feNO1) transformation, and deter-

mined in a consistent way by the spatial analysis of the(VNO¿ ,Ve,P) and (VN¿ ,Ve,P) vector correlations. The cor-respondingbA1'0.5 ~60.05! ion fragment asymmetry pa-rameter for the photon energyhn520.9 eV quantifies thedominant parallel character of the transition. The slightlynegativebe'20.2 ~60.05! electron asymmetry parametershows that the electron emission in the laboratory referenceframe is weakly anisotropic, consistent with thebe'20.2previous measurement of Carlsonet al.20

The results presented in Fig. 4 correspond to a completeenergy selection of the processes, Eq.~2! and Eq.~3!. SimilarFLN

NO1(ue) andFLNN1(ue) functions are obtained when an en-

ergy selection of the different vibrational levels of theNO1(X 1S1) and NO(X 2P) molecular states is performedin the KECDs, as well as when the N2O1

„C 2S1 (0,0,1)…level is selected. The negative value of theF22(ue) function~see also Fig. 8 later! raises a first question, since that,according to the general form of the MFPADs for photo-ionization of linear molecules,13 the N2O(X 1S1) toN2O1(C 2S1) photoionization transition from an initial neu-tral to a final ionic state of the sameS1 symmetry should becharacterized by a positiveF22(ue) function. We note that inthe investigation of 6s inner-valence shell ionization of N2Oby (e,2e) electron momentum spectroscopy,19 a p contribu-tion to the dominants character orbital was identified. It wasinterpreted as the signature of the excitation of aP satellitestate„(2p)21

…, predicted at 0.4 eV below theC 2S1 by themany-body Green’s function calculations of Domckeet al.16

This interpretation was compatible with the 1.8 eV energyresolution in the (e,2e) experiments. However, in the presentstudy, the assumption that a satellite peak ofP symmetrymight be quasidegenerated with theC 2S1(0,0,0) levelwithin the DEe'100 meV energy resolution, and wouldcontribute to the negative sign ofF22(ue), is very unlikely.Furthermore, a similar result forF22(ue) is obtained whenthe C 2S1(0,0,1) level is considered. One must then con-

sider the fact that the predissociation lifetime of theN2O1(C 2S1) might be a significant fraction of the rota-tional period of the N2O1 molecule and influence the mea-suredFLN(ue) function. On the other hand, the lifetime ofthe C 2S1 state certainly should not exceed a complete ro-tation period since~i! a clear molecular frame forward–backward~MF–FW–BW! electron emission asymmetry per-sists, as described by theF00(ue) andF20(ue) functions, and~ii ! theF21(ue) functions shows a complex oscillatory struc-ture. These would be washed out if several molecular rota-tions would occur prior to dissociation. These effects arediscussed in Sec. V.

Figure 5 displays the measuredI (ue ,fe) MFPADs thatcorrespond to the breaking of the N–N molecular bond, withthe z molecular axis oriented in the direction of the N(1)

fragment, for the three selected orientations of the moleculeparallel, at the magic angle, and perpendicular to the polar-ization axis. They vizualize the (ue ,fe) electron emissionanisotropies in the molecular frame. For the dominant paral-lel transition, electron emission is favored along thez mo-lecular axis, in the direction of the N fragment, and in thedirection perpendicular to thez axis. For the orientation atthe magic angle, the electron emission diagram is dragged ina direction between the molecular and the polarization axis,with intensity maxima in the (ue'20°, fe'0°), andalongthe ridge going continuously from the (ue'90°,fe'180°)to (ue'130°,fe'0°) directions, consistent with the com-plex F21(ue) dependence. When the molecular axis is per-pendicular to the polarization axis, electron emission pre-sents broad maxima in the directions (ue'45°, fe'0° and180°!, and (ue'135°,fe'90°) with a weak azimuthal de-pendence reflecting the evolution of theF22(ue) function.

For comparison with theI i(ue) andI'(ue) MFPAD typeof observables for the parallel and perpendicular transitionsusually addressed in the literature, these together withI M(ue) for the magic angle orientation, are simply derivedfrom the I (ue ,fe) functions after integration overfe , ac-cording to the following expressions:

I i~ue!5F00~ue!1F20~ue!,

I M~ue!5F00~ue!, ~4!

I'~ue!5F00~ue!21/2F20~ue!.

The I i(ue) MFPAD is shown in Fig. 6. TheA1–A6 co-efficients of its partial wave analysis in Legendre polynomialexpansionI (ue)5S0

2l max Al Pl(cosue) given in Table II re-veal the dominant contribution of electron partial waves up

FIG. 5. I (ue ,fe) MFPADs for pro-cess~2! corresponding to theFLN(ue)functions given in Fig. 4, for a mol-ecule oriented parallel~a!, at themagic angle~b!, and perpendicular~c!to the polarization axis. Thez molecu-lar axis is oriented in the direction ofthe N(1) fragment.

9253J. Chem. Phys., Vol. 117, No. 20, 22 November 2002 Dissociative photoionization of N2O

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to l 52. The significant positiveA1 coefficient (A1'30%)reflects the preferred electron emission in the direction of theN fragment and quantifies the MF–FW–BW asymmetry thatcharacterizes the emission along the molecular axis. We notethat this asymmetry was not observed in the PEPICO resultsof Kinmondet al.4 under HeI excitation (hn521.2 eV). TheI M(ue) and I'(ue) polar angle MFPADs obtained after inte-gration over thefe azimuthal angle, and the result of thepartial wave analysis of these functions in Legendre polyno-mial expansion, are also displayed in Fig. 6 and Table II forcompleteness.

We have performed the vector correlation analysis ofthe above processes@Eqs. ~2! and ~3!# in the 20.5 eV<hn<22.5 eV photon energy range, with increasing extractionfields. TheF00(ue) andF20(ue) functions display very simi-lar shapes as those presented for the 20.9 eV photon energy.The relative importance ofF20(ue) with respect toF00(ue)increases with photon energy, which corresponds to a de-crease of thebNO1/N1 asymmetry parameter, frombA1

'0.5 at 20.5 eV tobA1'0.15 at 22.5 eV. On the other hand,the be asymmetry parameter increases frombe'20.2 tobe'0, consistent with the results of angular-resolved photo-electron spectroscopy.20 For hn'21.2 eV and above theF21(ue) function referred to the N fragment keeps the sameoscillatory structure taking now only positive values, whiletheF22(ue) function becomes slightly positive too. We pointout that the observed energy dependence of theFLN(ue)functions is found identical when analyzing the two DPI pro-cesses in Eqs.~2! and~3!, leading to the NO1 and N1 frag-ments, respectively.

The experimental determination of the MFPADs for theweaker DPI processes leading to the N2

1 and O1 fragments,for which theEA1 kinetic energy is smaller, is achieved withlower precision. At this level of the analysis, the onlyFLN(ue) functions taking significant values are the twoF00(ue) functions. F00(ue)(N2

1) gradually decreases whenue ~referred to as the N2

1 emission direction! increases from0° to 180° while, consistently,F00(ue)(O

1) gradually in-creases whenue ~referred to as the O1 emission direction!increases from 0° to 180°. So, although the information ismore limited, these data also indicate a preferred electronemission in the molecular frame in the direction of the N endof the molecule.

V. COMPUTED MFPADs AND DISCUSSION

The FLN(ue) functions for ionization leading to theC 2S1 state of N2O1 were computed using the multichannelSchwinger configuration interaction~MCSCI! method. Thegeometry was taken to haveRN–N51.1282 Å andRN–O

51.1842 Å.29 The molecular orbitals used to represent thebound states were expanded in the correlation-consistent po-larized valence triple zeta basis set augmented with diffusefunctions~aug-cc-pVTZ! of Dunning.30,31In this basis set theground state self-consistent-field energy was2183.751464au. The orbitals used in the MCSCI calculation were thenatural orbitals obtained from a complete-active-space self-consistent-field calculation~CASSCF! on the ground state ofN2O with five cores orbitals, four actives orbitals, andthree activep orbitals. The CASSCF calculations were per-formed using theMOLPRO program.32 The CASSCF groundstate energy was2183.928 238 a.u. These orbitals were thenused in a limited configuration interaction~CI! calculation toobtain a compact representation for the initial and ion statesof N2O. For the initial state, the configurations included atmost three electrons in the two most weakly occupiedsorbitals and at most four electrons in the two most weaklyoccupieds orbitals and the most weakly occupiedp orbital.The ion states were computed using configurations that had,at most two electrons in the two most weakly occupiedsorbitals and, at most three electrons in the two most weaklyoccupieds orbitals and the most weakly occupiedp orbital.The CI was performed using the same single-center expan-sion techniques as was used for the photoionizationcalculation.21 In the single-center expansions for both the CIand MCSCI calculations, all orbitals were expanded up tol maxorbital580 and the potentials were then expanded up to

l maxpotential5160. The maximuml included in the expansion of

the homogeneous solutions wasl maxhomo511. The computed

vertical ionization potentials were then 12.80, 16.45, 18.55,and 20.65 eV for the X 2P(2p21), A 2S1(7s21),B 2P(1p21), and C 2S1(6s21) states of N2O1, respec-tively. These values compare favorably with the values com-puted with the outer valence-type many-body Green’s func-tion techniques16 of 12.72, 16.38, 18.93, and 20.53 eV, andwith the experimental vertical ionization potentials15,16 of12.9, 16.5, 18.3, and 20.1 eV. We also find a low-lyingsatellite state of2P symmetry at 20.91, i.e., 0.26 eV abovethe C 2S1(6s21) state. Domckeet al.16 also found such a

FIG. 6. I i(ue) ~—d—!, I M(ue) ~—j—!, I'(ue) ~—s—! MFPADs forprocess~2! corresponding to theFLN(ue) functions given in Fig. 4, obtainedafter integration over thefe azimuthal angle.ue is referred to the directionof the N(1) fragment.

TABLE II. The A1–A6 coefficients of the partial wave analysis in Legendrepolynomial expansions of theI i(ue), I M(ue), and I'(ue) MFPADs shownin Fig. 6. A0 is normalized to 1.

A1 I i I M I'

1 0.3660.01 0.3260.01 0.2860.012 20.3760.01 20.1760.01 0.0160.013 0.1560.01 0.0560.01 20.0460.014 0.2560.01 0.0760.01 20.1060.015 0.0260.01 0.0160.01 20.0160.016 0.0260.01 0.0060.01 20.0260.01

9254 J. Chem. Phys., Vol. 117, No. 20, 22 November 2002 Lebech et al.

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low-lying satellite state 0.30 eV above theC 2S1(6s21)state. In all of the photoionization calculations we includedfive states: X 2P(2p21), A 2S1(7s21), B 2P(1p21),C 2S1(6s21), and 32P(1p21 satellite), in the expansionof the scattering wave function. To compare with the experi-mental data for ionization leading to the~0, 0, 0! vibrationalstate of theC 2S1(6s21) state obtained at a photon energyof 20.9 eV, we computed our cross sections at a photon en-ergy of 21.5 eV, which yields a photoelectron energy of 0.85eV that is close to the asymptotic experimental photoelectronenergy of 0.79 eV. In the calculation of the effects of rotationon the MFPAD of theC state, we used the ground staterotation constant29 0.419 011 cm21 for both the ground stateand theC ion state, and a rotational temperature of 35 K.

The computedFLN(ue) functions displayed in Fig. 7 cor-respond to aue polar angle defined with respect to the O endof the molecule. They reveal similar features, as found ex-perimentally for the two studied DPI processes, Eq.~2! andEq. ~3!. The comparison must be made with Fig. 5~a!, whichcorresponds to aue polar angle defined with respect to theNO1 fragment emission direction. A strong MF–FW–BWasymmetry favoring electron emission in the direction of theN fragment is illustrated by theF00(ue) and F20(ue) com-puted functions. The calculations also reproduce the maincharacteristic oscillations ofF21(ue), although the zero ofthe first oscillation occurs atue575° for the computed curveand atue590° in the experimental curve. However, we alsonotice significant differences:~i! The oscillatory structure ofthe calculatedF00(ue) andF20(ue) functions is much morepronounced than in that obtained experimentally;~ii ! the cal-

culated F22(ue) function is positive, consistent with theN2O(X 1S1) to N2O1(C 2S1) photoionization transitionconsidered~see also Fig. 8!.

The effects of the instrumental widths defining the appa-ratus function have been studied using a Monte Carlo simu-lation of the experiment.11–13 They are small in the presentexperimental conditions due to the use of theL1 and Le

focusing lens sets and a proper optimization of the molecularbeam expansion: the modifications induced on the computedFLN(ue) functions are minor with respect to the differencesfound between experimental and theoretical values. There-fore we have investigated the influence of a finite lifetime ofthe C state on the structure of theFLN(ue) functions.

The effect of molecular rotation due to a finite lifetimeof the ionic state has been studied by performing a quantalcalculations of theFLN

Q (ue) functions as described in Ref. 33.The evolution of the selectedF00(ue) andF22(ue) functionswith the predissociation time (t50, 1 ps, 2 ps, and infinite!is presented in Fig. 8, where the calculated values are com-pared with the measured ones. They appear as a sensitiveprobe of the predissociation lifetime. We observe that for alifetime of the order oft'2 ps a nice, although not perfect,agreement is found between the experimental and theoreticaldata: for example, the FW–BW asymmetry found experi-mentally in F00(ue) is larger than the one remaining in thecomputed value after rotation has been taken into account.Consistently, the calculatedbA1 asymmetry parameter thatvaries between 1.65 (t50) to 0.41~t infinite!33 correspondsto the measuredbA1'0.5 value fort of about 2 ps. Thisvalue corresponds to approximately 1/4 of the rotational pe-riod. It will be interesting to compare the present estimationof the lifetime of the N2O1(C 2S1) state with the value thatcan be derived from the high-resolution pulsed field ioniza-tion photoelectron study34 of N2O.

The results obtained for the N21 and O1 fragments,

though with limited statistics, indicate a different behavior ofthe FLN(ue) for the breaking of the N–O bond in the N2Omolecule. This feature would require further theoretical in-vestigation.

Finally, we present in Fig. 9 the computedI xA1(ue ,fe)MFPADs, for the three selected orientations of the moleculeparallel, at the magic angle, and perpendicular to the polar-ization axis, ignoring rotation~a!, and assuming a lifetimet52 ps ~b!. This figure vizualizes in the three-dimensionalrepresentation the smoothing of the MFPADs introducedwhen the lifetime of the predissociative state is a sig-

FIG. 7. FNL(ue) functions for photoionization into the N2O1(C 2S1) statecomputed using the MCSCI method at hn521.5 eV(—,F00 , – – – ,F20 ;---,F21 ;¯ ,F22) for t50. ue is defined with respect tothe O end of the N2O molecule.

FIG. 8. F00(ue) andF22(ue) functionsfor photoionization into theN2O1(C 2S1) state computed for dif-ferent lifetimes of theC state: witht50 ~—!, 1 ps ~–––!, 2 ps ~---!, andinfinite ~¯!, compared with the mea-sured F00(ue) and F22(ue) distribu-tions ~—d—!. The experimental andtheoretical data are normalized by ad-justing the total photoionization crosssection for this process.ue is definedwith respect to the O end of the N2Omolecule.

9255J. Chem. Phys., Vol. 117, No. 20, 22 November 2002 Dissociative photoionization of N2O

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nificant fraction of the rotational period. Figure 9~b! com-pares well with the experimental result presented in Fig. 5.Figure 9~a! illustrates the structure of the nascent MFPADs:the electron emission pattern in the molecular frame is domi-nated by ads partial wave for the parallel transition and adp partial wave for the perpendicular transition, where itexhibits the strong cos2 fe dependence characteristic of aS1

to S1 photoionization transition.

VI. CONCLUSION

In this paper, the (VA¿ ,Ve,P) vector correlation methodhas been extended to the investigation of dissociative photo-ionization of the N2O linear molecule, illustrated by photo-ionization via the N2O1(C 2S1) ionic state. The ion–electron kinetic energy correlation diagrams enable theidentification of all the DPI processes producing the NO1,N1, N2

1 , and O1 fragments. The resolution of the vibra-tional distribution of the NO(X 2P,v) molecular fragment inthe @NO(X 2P,v)1N1(3P)# outgoing channel is achieved.

The MFPADs characterizing the breaking of the N–Nbond in the N2O1(C 2S1) molecular ion exhibit remarkablefeatures, revealed in a consistent way by the (VNO¿ ,Ve,P)and (VN¿ ,Ve,P) vector correlation analyses. The polar de-pendence of the MFPAD for the dominant transition, whichcorresponds to photoabsorption by a molecule aligned paral-lel to the polarization axis, demonstrates a preferred electronemission from the N2O1 molecular ion in the direction per-pendicular to the molecular axis, as well as a strongforward–backward asymmetry, which favors electron emis-sion along the molecular axis in the same direction as the N1

or N fragment. The main characteristics of the electron emis-sion pattern in the molecular frame are well predicted by thereported MCSCI calculations for photoionization into theN2O1(C 2S1) state. The measured and calculated MFPADsare found in good agreement when the rotation of the mo-lecular ion prior to dissociation is taken into account. This

comparison provides an estimation of the lifetime of theN2O1(C 2S1) state, prior to dissociation into the dominantchannels @NO1(X 1S1)1N(2P)# and @N1(3P)1NO(X 2P)#, which is found to be about 2 ps.

The level of agreement found here between the com-puted and measured MFPADs was obtained with a relativelylimited calculation~only five channels! and using an easilycomputed set of molecular orbitals~from the CASSCF cal-culation on the ground state!. The simplicity of the channelexpansion used here is in contrast to the 17-channel calcula-tion required to obtain a similar level of agreement in ourprevious study13 of the MFPAD of NO. Of course, an impor-tant difference between these two molecules is that theclosed shell N2O molecule has a much simpler and sparsermanifold of low-lying ion states than does NO.

Note added in proof.Related experimental work hasbeen reported recently by Hikosaka and Eland.35

ACKNOWLEDGMENTS

The authors are grateful to Professor C. Y. Ng for fruitfulexchanges involving PFI-PE results prior to publication, andto Professor A. Beswick for useful discussions. We gratefullyacknowledge the help of Dr. C. Alcaraz~line SA63!, Dr. L.Nahon~line SU5!, and Dr. M. Elhanine~SAPHIRS!, as wellas the assistance of B. Pilette and co-workers at LURE. Thesupport of the National Science Foundation~USA!, throughGrant No. INT-0089831, and of the Center National de laRecherche Scientifique~France! are gratefully acknowl-edged. This work was in part supported by the Welch Foun-dation under Grant No. A-1020 and also by the Texas A&MUniversity Supercomputing Facility.

1D. Dill, J. Chem. Phys.65, 1130~1976!.2R. N. Zare, J. Chem. Phys.47, 204 ~1967!.3I. Powis, J. Chem. Phys.99, 3436~1993!.4E. Kinmond, J. H. D. Eland, and L. Karlsson, Int. J. Mass. Spectrom.185Õ186Õ187, 437 ~1999!, and references therein.

FIG. 9. ComputedI (ue ,fe) MFPADsfor a molecule oriented parallel, at themagic angle, and perpendicular to thepolarization axis, corresponding to theFLN(ue) functions displayed in Fig. 8,for t50 ps ~a! andt52 ps ~b!. The zmolecular axis is oriented in the direc-tion of the N(1) fragment.

9256 J. Chem. Phys., Vol. 117, No. 20, 22 November 2002 Lebech et al.

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5P. Downie and I. Powis, Phys. Rev. Lett.82, 2864~1999!.6Y. Hikosaka, J. H. D. Eland, T. M. Watson, and I. Powis, J. Chem. Phys.115, 4593~2001!.

7N. Watanabe, J. Adachi, K. Soejima, E. Shigemasa, A. Yagishita, N. G.Fominykh, and A. A. Pavlychev, Phys. Rev. Lett.78, 26 ~1997!.

8R. E. Continetti, Annu. Rev. Phys. Chem.52, 165 ~2001!, and referencestherein.

9J. A. Davies, R. E. Continetti, D. W. Chandler, and C. C. Hayden, Phys.Rev. Lett.84, 5983~2000!.

10K. L. Reid, T. A. Field, M. Towrie, and P. Matousek, J. Chem. Phys.111,1438~1999!; M. Tsubouchi, B. J. Whitaker, L. Wang, H. Kohguchi, and T.Suzuki, Phys. Rev. Lett.86, 4500~2001!.

11A. Lafosse, M. Lebech, J. C. Brenot, P. M. Guyon, O. Jagutski, L. Spiel-berger, M. Vervloet, J. C. Houver, and D. Dowek, Phys. Rev. Lett.84,5987 ~2000!.

12A. Lafosse, J. C. Brenot, A. Golovin, P. M. Guyon, K. Hoejrup, J. C.Houver, M. Lebech, and D. Dowek, J. Chem. Phys.114, 6605~2001!.

13R. Lucchese, A. Lafosse, J. C. Brenot, P. M. Guyon, J. C. Houver, M.Lebech, G. Raseev, and D. Dowek, Phys. Rev. A65, 020702~2002!.

14For a recent review see, e.g., P. Rosmus and G. Chambaud,Photoioniza-tion and Photodetachment, Advanced Series in Physical Chemistry, editedby C. Y. Ng ~World Scientific, Singapore, 2000!, Vol. 10A, p. 182.

15D. W. Turner, C. Baker, A. D. Baker, and C. R. Brundle,Molecular Pho-toelectron Spectroscopy~Wiley-Interscience, London, 1970!.

16W. Domcke, L. S. Cederbaum, J. Schirmer, W. Von Niessen, C. E. Brion,and K. H. Tan, Chem. Phys.40, 171 ~1979!, and references therein; H.Nakatsuji,ibid. 75, 425 ~1983!.

17G. Chambaud, H. Gritli, P. Rosmus, H.-J. Werner, and P. J. Knowles, Mol.Phys.98, 1793~2000!.

18A. W. Potts and T. A. Williams, J. Electron Spectrosc. Relat. Phenom.3, 3~1974!; D. M. P. Holland, M. A. MacDonald, and M. A. Hayes, Chem.Phys.142, 291 ~1990!.

19R. Fantoni, A. Giardini-Guidoni, R. Tiribelli, R. Camilloni, and G. Stefani,Chem. Phys. Lett.71, 335~1980!; A. Minchinton, I. Fuss, and E. Weiglod,J. Electron Spectrosc. Relat. Phenom.27, 1 ~1982!.

20T. A. Carlson, P. R. Keller, J. W. Taylor, T. Whitley, and F. A. Grimm, J.Chem. Phys.79, 97 ~1983!.

21R. R. Lucchese, K. Takatsuka, and V. McKoy, Phys. Rep.131, 148~1986!;R. E. Stratmann and R. R. Lucchese, J. Chem. Phys.102, 8493~1995!; R.E. Stratmann, R. W. Zurales, and R. R. Lucchese,ibid. 104, 8989~1996!.

22D. A. Shaw, D. M. P. Holland, M. A. MacDonald, A. Hopkirk, M. A.Hayes, and S. M. McSweeney, Chem. Phys.163, 387~1992!; M. Ukai, K.Kameta, S. Machida, N. Kouchi, Y. Hatano, and K. Tanaka, J. Chem.Phys.101, 5473 ~1994!; E. Sokell, A. A. Wills, J. Comer, and P. Ham-mond, J. Phys. B30, 2635~1997!, and references therein.

23P. M. Dehmer, J. L. Dehmer, and W. A. Chupka, J. Chem. Phys.73, 126~1980!.

24J. Berkowitz and J. H. D. Eland, J. Chem. Phys.67, 2740~1977!.25T. Masuoka and S. Mitani, J. Chem. Phys.90, 2651~1989!.26I. Nenner, P. M. Guyon, T. Baer, and T. R. Govers, J. Chem. Phys.72,

6587 ~1980!; S.-Y. Chiang and C.-I. Ma, J. Phys. Chem. A104, 1991~2000!.

27M. Richard-Viard, A. Delboulbe´, and M. Vervloet, Chem. Phys.209, 159~1996!.

28M. Lebech, J. C. Houver, and D. Dowek, Rev. Sci. Instrum.73, 1866~2002!.

29G. Herzberg,Molecular Spectra and Molecular Structure, Vol. III—Electronic Spectra and Electronic Structure of Polyatomic Molecules~VanNostrand, Princeton, 1966!.

30T. H. Dunning, Jr., J. Chem. Phys.90, 1007~1989!.31R. A. Kendall, T. H. Dunning, Jr., and R. J. Harrison, J. Chem. Phys.96,

6796 ~1992!.32MOLPRO, a package ofab initio programs designed by H.-J. Werner and

P. J. Knowles, version 2000.1, R. D. Amos, A. Bernhardsson, A. Berninget al., Birmingham, UK, 2000.

33A. Lafosse, J. C. Brenot, A. Golovin, P. M. Guyon, J. C. Houver, M.Lebech, P. Lin, R. R. Lucchese and D. Dowek, J. Chem. Phys.~to bepublished!.

34C. Y. Ng ~private communication!.35Y. Hikosaka and J. H.-D. Eland, Chem. Phys.281, 91 ~2002!.

9257J. Chem. Phys., Vol. 117, No. 20, 22 November 2002 Dissociative photoionization of N2O

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