Laserinduced fluorescence study of the reaction C(3 P)+HI→CH(X 2Π)+I at 300 KNobuaki Nishiyama, Hiroshi Sekiya, and Yukio Nishimura Citation: The Journal of Chemical Physics 84, 5213 (1986); doi: 10.1063/1.450640 View online: http://dx.doi.org/10.1063/1.450640 View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/84/9?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Laserinduced fluorescence study of the reactions Cu+X2→CuX+X (X=F, Cl, Br, and I) J. Chem. Phys. 95, 6413 (1991); 10.1063/1.461561 A laserinduced fluorescence study of product rotational state distributions in the charge transfer reaction:Ar+(2 P 3 / 2)+N2→Ar+N+ 2 (X) at 0.28 and 0.40 eV J. Chem. Phys. 90, 1677 (1989); 10.1063/1.456673 A study of the reaction Li+HCl by the technique of timeresolved laserinduced fluorescence spectroscopy ofLi (22 P J –22 S 1 / 2, λ=670.7 nm) between 700 and 1000 K J. Chem. Phys. 87, 4606 (1987); 10.1063/1.452871 The dynamics of the reactions F+IX→IF+X (X=Cl, Br, I): A laserinduced fluorescence study J. Chem. Phys. 78, 6091 (1983); 10.1063/1.444570 Laserinduced fluorescence study of the reactions of F atoms with CH3I and CF3I J. Chem. Phys. 72, 1128 (1980); 10.1063/1.439254

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Letters to the Editor

to 60 amagats which further flattens the structures. It is, therefore, not surprising that the measurement does not re­veal dimer features. H2-N2 dimer spectra were seen under more favorable conditions in the fundamental band. 16

.) The support of the NSF, grant AST-8310786, for the work at the Univer-sity of Texas is acknowledged.

IH. L. Welsh, MTP Int. Rev. SeL, Phys. Chem., Ser. 1, Vol. 3,1972. 2W. Meyer, in Phenomena Induced by Intermolecular Interactions, edited by G. Birnbaum (Plenum, New York, 1985).

3K. C. Hunt, in Ref. 2. 41. van Kranendonk, Physica 25,337 (1959). 'I. Borysowand L. Frommhold, in Ref. 2. 6A. Watanabe and H. L. Welsh, Can. 1. Phys. 45, 2859 (1967). 7R. A. Samuelson, R. A. Hanel, V. G. Kunde, and W. C. Maguire, Nature 292,688 (1981).

8 A. Borysow and L. Frommhold, Astrophys. 1. (to be published). 'T. Codastefano and P. Dore, 1. Quant. Spectrosc. Radiat. Transfer (to be published).

lOG. C. Maitland, M. Rigby, E. B. Smith, and w. A. Wakeham, Intermole­cular Forces, TheirOrigin and Determination (Clarendon, Oxford, 1981).

IIR. D. McCarty, 1. Hord, and H. M. Roder, Nat!. Bur. Stand. Monogr. 168 (1981).

12R. T.Iacobsenand R. B. Stewart, 1. Phys. Chern. Ref. Data 2, 757 (1973). l3p. Dore, L. Nencini, and G. Birnbaum, 1. Quant. Spectrosc. Radiat.

Transfer 61, 591 (1983). 14p. Codastefano, P. Dore, and L. Nencini, 1. Quant. Spectrosc. Radiat.

Transfer (in press). I'W. Meyer and L. Frommhold (in preparation). 16A. Kudian, H. L. Welsh, and A. Watanabe, J. Chern. Phys. 47, 1553

( 1967). 17We note that the values of the hydrogen quadrupole and hexadecapole

moments, 0.48729 ea5 and 0.3530 ea~, were taken from 1. D. Poll and L. Wolniewicz, 1. Chern. Phys. 68, 3053 (1978) and G. Karl, J. D. Poll, and L. Wolniewicz, Can. J. Phys. 53, 1781 (1975), respectively. The corre­sponding values of N2, - 1.09 ea~ and - 10.4 ea~, are from A. D. Buckingham, C. Graham, and J. H. Williams, Mol. Phys. 49, 703 (1983) and 1. D. Poll and J. L. Hunt, Can. J. Phys. 59,1448 (1981), respectively. More details can be found in Ref. 8.

Laser-Induced fluorescence study of the reaction C(3P) + HI~CH(X 2II) + I at 300 K

Nobuaki Nishiyama, Hiroshi Sekiya, and Yukio Nishimura Department of Molecular Science and Technology, Graduate School of Engineering Sciences, and Research Institute of Industrial Science, Kyushu University, Kasuga-shi, Fukuoka. 816, Japan

(Received 16 January 1986; accepted 29 January 1986)

The hydrogen atom abstraction reactions ofC(3p) and Oe P) are important in combustion and atmospheric chem­istry. The reaction dynamics of O( 3 P) atoms with diatomic 1

and polyatomic2~ molecules have been studied extensively by measuring the internal energy state distributions of OH radicals. However, little is known on the reaction of C( 3 P) atoms. In this note, we first report the observation of CH radicals from the reaction of Cep) atoms with HI mole­cules. Among the Cep) + HX (X = CI, Br, I) reactions, only the C(3P) + HI reaction is exoergic enough for pro­ducing the CH radicals at 300 K. The vibrational distribu­tion of CH(X 2n) was determined by using the laser-in­duced fluorescence (LIF) technique and the reaction dynamics ofC(3p) atoms was discussed.

Experiments were carried out by using a flowing after­glow apparatus coupled with LIF detection system, which has been essentially identical to that used for the Cep) + NO and Cep) + N20 reactions.7 Briefly, the Cep) atoms were produced from the dissociation of CO molecules by Arep2,0) atoms:

(1)

Since the dissociation energy of CO is 11.09 eV,8 Arep 2,0) ep2 = 11.55, 3PO= 11.72 eV) are insufficient to produce the metastable state carbon atoms. Ar( 3 P 2,0 ) was generated by a hollow cathode discharge of Ar gas. The absence of argon ion (Ar+) and argon metastable ion (Ar + M) under operating condition was confirmed from the nonobservation of the OCS+(,A 2n_1'2n)9 and CH(A 2a_X2n) emission spectralO resulting from the Ar+ + OCS and Ar+ M + CH3CN reactions, respectively. The HI gas was prepared from the desiccation of hydriodic acid with P 20S

and introduced through a glass nozzle placed 10 cm down­stream from the CO gas inlet.

The CH (X 2n) radicals produced were probed by a N2 laser pumped dye laser source (Molectron UV22-DL14P). The fluorescence signal from a photomultiplier (HTV R955) was amplified with a preamplifier (NF BX-31) and averaged by a boxcar integrator (NF BX-531). The av = 0 sequence of the CH (A-X) transition was excited and the fluorescence of the av = 0 or av = - 1 sequence was de­tected through an interference filter centered at 487 nm (FWHM = 20 nm). The Ar pressure was varied from 0.15 to 0.20 Torr, while the CO and HI pressures ranged from 1 to 20mTorr.

J. Chern. Phys. 84 (9),1 May 1986 0021-9606/86/095213-02$02.10 @ 1986 American Institute of PhysiCS 5213 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:

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5214 Letters to the Editor

A typical CH(A-X) LIF spectrum is shown in Fig. 1. A small amount of H2 and H20 molecules may be involved in the sample gas due to the photodecomposition or oxida­tion of HI. However, the formation ofCH radicals from the reactions ofC( 3 P) with H2 and H20 is endoergic. Therefore, it was concluded that the CH (X) radicals were formed from the reaction ofCep) with HI:

Cep) +HIel:+)-+CH(X 2n) + Iep3/2 ),

MI = - 0.48 eV . (2)

The formation ofIepl /2) as a partner ofCH(X 2n) is 0.46 e V endoergic. As is clear from Fig. I, CH (X) is produced in the vibrational level v" = 0 and 1. The formation of the v" = 2 level is 0.18 e V endoergic and this level was not de­tected.

The rotational distribution of the observed CH(A-X) LIF spectrum is expressed well by a Boltzmann distribution at 300 K, indicating complete thermalization of rotational distribution by collisions with Ar, CO, and HI gases. The relative vibrational populations of CH(X) was determined by a similar procedure to that described previously.? Accu­rate determination of the relative vibrational population of v" = 1 was difficult from the LIF spectrum obtained from the Av = 0 excitation and the Av = - 1 detection since the Franck-Condon factors of the Av = - I sequence are ex­tremely small compared with those of the Av = 0 se­quence. 11 Then, the relative vibrational population of CH (X) was measured from the LIF spectrum obtained from monitoring fluorescence of the Av = 0 sequence, although the signal-to-noise ratio is much lower than the former LIF spectrum. In order to determine the nascent vibrational dis­tribution of CH(X), the vibrational relaxation of CH(X, v" = 1) was investigated as a function of partial pressures of Ar, HI, or CO gas. It has been found that the vibrational relaxation of CH (X, v" = 1) by collisions with Ar and HI is very small, while relatively large vibrational relaxation owing to the collisions with CO has been observed. The nas­cent vibrational populations of CH(X, v" = 1) have been determined by smoothly extrapolating the population ratio v" = l/v" = 0 to zero CO pressure, since the ratio increased gradually with decreasing CO pressure. The vibrational population of v" = 1 was estimated to be 45 ± 4% of that of v" = 0, while the statistical estimate by prior calculation predicts much smaller vibrational excitation (15%). By us­ing these values, the fraction of available energy deposited in vibration, (Iv), was estimated to be 0.31 ± 0.02.

The reactions of the ground-state F, CI, and 0 atoms with HI have been studied extensively by observing the in­frared chemiluminescence. 1

,12 For the above reactions, a very large fraction of the available energy is channeled into HP, HCI, and OH «Iv) =0.59-0.67). The similarity in vibrational energy disposal was interpreted as a consequence of the mass combination H + LH, which can override small difference in potential energy for direct transfer. 1 Parr et al. have applied the classical trajectory method to the CI + HI reaction. 13 It was suggested that the mass combination

(0,0) f Rl

, 3

l'R2 (1,1) Q head • 3 lQ21 ~O, 0) , 3'

(1,1) 2' f Rl

2' 1 ·R2

FIG. 1. CH(A+-X) LIF spectrum observed from the cC P) + Hlreaction. Experimental conditions were Ar: 0.2 Torr, CO: 6 mTorr, and HI: 1 mTorr.

H + LH on a highly repulsive surface was responsible for the high vibrational excitation of HCI.

The lower (/v(CH» than (/v(HF», (Iv (HCl), and (I v (OH» suggests that dynamic (potential-energy dependent) effect as well as kinematic (mass-dependent) effect is important for the vibrational excitation of CH (X). In order to give a definite conclusion for the reaction dynam­ics, the other experimental observations such as the rota­tional distribution and the angular distribution of CH(X) are necessary.

This work was supported by a Grant-in-Aid for Scientif­ic Research from the Ministry of Education, Science, and Culture.

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7H. Sekiya, M. Tsuji, and Y. Nishimura, J. Chem. Phys. 84, 3739 (1986). 8K. P. Huber and G. Herzberg, Constants of Diatomic Molecules (Van Nostrand, Princeton, 1979).

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101. Nishiyama, Y. Ozaki, K. Suzuki, and K. Kuchitsu, Chem. Phys. Lett. 67,258 (1979).

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J. Chern. Phys., Vol. 84, No.9, 1 May 1986

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