Journal of Molecular Spectroscopy 221 (2003) 149–155
www.elsevier.com/locate/jms
Rotational spectrum of CoF in the X3U4 electronic ground state
Toshiaki Okabayashi* and Mitsutoshi Tanimoto
Department of Chemistry, Faculty of Science, Shizuoka University, Oya 836, Shizuoka 422-8529, Japan
Received 3 March 2003; in revised form 25 June 2003
Abstract
The rotational spectrum of the CoF radical in the X 3U4 state was observed by employing a source modulation microwave
spectrometer. The CoF radical was generated in a free space cell by a dc glow discharge in CF4 and He. The cobalt atoms were
supplied by the sputtering reaction from cobalt powder placed over a lower surface of the cylindrical electrodes. The transitions with
J ¼ 11–10 to 17–16 were measured in the region between 250 and 400GHz. The effective rotational, centrifugal distortion, and
hyperfine constants were obtained by a least-squares analysis.
� 2003 Elsevier Inc. All rights reserved.
1. Introduction
Transition metal compounds have often high elec-
tronic-orbital and electron spin angular momenta due totheir d-electrons. The d-electrons thus cause a large
number of low lying electronic excited states. These elec-
tronic states and their substates result in remarkably
complex spectra observed by a high resolution spectro-
scopic method. It is interesting to observe high resolution
spectrum of such species in order to understand their
electronic properties fromanalysis of hyperfine constants.
However, it is difficult to produce the transition metalcompounds in the gas phase abundantly enough to ob-
serve rotational spectrumwhich is oneof themost suitable
method to observe hyperfine-resolved spectrum. Thus,
the electronic spectra with unresolved hyperfine structure
have been mainly employed to study such species [1,2].
The diatomic transition metal halides MX (M¼transition metal; X¼F, Cl, Br, and I) are highly ionic
species represented as MþX�. All unpaired electronsmainly exist on the metal atom because of the closed
shell structure of the X� ion. The electronic states
strongly reflect the character of metal ions Mþ. Thus,the transition metal halide is one of the simplest pro-
totypes to understand metal–ligand bonding.
Cobalt monofluoride (CoF) is one of such halides
that have scarcely been studied by any spectroscopic
* Corresponding author. Fax: +81542373384.
E-mail address: [email protected] (T. Okabayashi).
0022-2852/$ - see front matter � 2003 Elsevier Inc. All rights reserved.
doi:10.1016/S0022-2852(03)00201-7
methods until recently. However, the electronic spectra
of CoF have been studied by two groups lately. The first
reliable spectrum was reported by Adam et al., who
observed the visible [18.8]3Ui–X 3Ui transition with highresolution LIF spectroscopy and carried out the rota-
tional analysis, initially using a Hund�s case (c) basis set[3] and later a case (a) basis set [4]. Ram et al. [5,6] re-
ported high resolution Fourier transform spectrum of
the C3Di–X 3Ui, D3Di–X 3Ui, G3Ui–X 3Ui, and G3Ui–C3Di
bands in the near-infrared region.
Recently, we have carried out millimeter- and sub-
millimeter-wave spectroscopic studies on several transi-tion metal halides such as CrF(X 6Rþ) [7], FeCl(X 6Di)
[8], NiF(X 2Pi) [9], and CuF (X 1Rþ) [10] which were
efficiently generated by the sputtering reaction of
metallic targets. As an extension of our interest in
transition metal halides, we report millimeter- and sub-
millimeter-wave spectroscopy of the CoF (X 3Ui) radical
in the present paper.
2. Experimental
The present experiment was carried out using a source-
modulated microwave spectrometer [11]. Millimeter- and
submillimeter-wave radiations were generated by multi-
plying the output of klystrons. The radiation transmitted
through a free space cell was detected by an InSb detectorcooled at 4.2 K by liquid helium. The cell contained a pair
of cylindrical electrodes for a dc glow discharge. The cell
395268.5 (MHz) 395274.5
CoF (X 3Φ4) J=17-16 F1=19.5-18.5
F=20-19 F=19-18
Fig. 1. Rotational transitions of CoF in the ground X 3U4 states.
Table 1
Molecular constants of CoF (X 3U4)a
MW NIRb
B0 (MHz) 11635.32099(51) 11635.422(39)
D0 (kHz) 15.3437(10) 15.3553(26)
H0 (mHz) )6.038c )6.038(48)
150 T. Okabayashi, M. Tanimoto / Journal of Molecular Spectroscopy 221 (2003) 149–155
was surrounded by Helmholtz coils in order to cancel the
magnetic field of the Earth.
The CoF radical was generated in the free space cellby a dc glow discharge in CF4 and He. The cobalt atoms
were supplied by the sputtering reaction from cobalt
powder scattered over the lower surface of the elec-
trodes. The transition frequencies were predicted from
molecular constants recently obtained from the elec-
tronic spectra [5,6]. First we searched for the J ¼ 16–15
transition of the CoF radical in the lowest X 3U4 spin
component near 372GHz. Sixteen lines which showedremarkably paramagnetic behavior were observed be-
tween 372 025 and 372 140MHz. These lines appeared
when the cell temperature was below )150 �C and the
discharge current was above 300mA. With cooler cell
temperature and higher discharge current, the lines were
stronger. Accordingly the cell was cooled to the liquid
nitrogen temperature and the discharge current was set
to about 500mA. Optimum sample pressure was5mTorr of CF4 and 30mTorr of He. Under this con-
dition, the spectral lines were quenched within a minute
after the discharge was started.
If the carrier of these paramagnetic lines was the CoF
radical, it was quite reasonable that the 16 lines were
caused by the hyperfine interactions fromboth cobalt and
fluorine nuclei.Moreover,weobservedother J transitionsdue to this carrier, and therefore this specieswas identifiedas the CoF radical. No spectral lines were detected in the
higher spin substates, X 3U3 and X 3U2, which are, re-
spectively, located about 700 and 1400 cm�1 above the
lowest X 3U4 substate [4], because the signal-to-noise ratio
was poor. Finally, we observed 90 lines from J ¼ 11–10 to
17–16 transitions in the region between 250 and 400GHz.
Fig. 1 shows an example of the observed spectral line.
h4(Co) (MHz) 974.9(18)h4D(Co) (MHz) )0.1675(11)eQq(Co) (MHz) )77.50(91)h4(F) (MHz) 233.52(32)aValues in parentheses are one standard deviation.bRef. [6].c Fixed in the analysis.
3. Analysis
The observed transition frequencies were analyzed by
a least-squares analysis using a Hund�s case (c) effective
Hamiltonian with two nonzero spin nuclei. The couplingscheme is F1 ¼ J þ ICo and F ¼ F1 þ IF.
The Hamiltonian employed is
Heff ¼ Hrot þ Hhf ; ð1Þwhere Hrot represents rotational energy including
centrifugal distortion, and Hhf hyperfine interaction. The
matrix elements are described as follows [12,13]:
hJXF1F jHrotjJXF1F i ¼ B0JðJ þ 1Þ � D0J 2ðJ þ 1Þ2
þ H0J 3ðJ þ 1Þ3 ð2Þ
and
hJ 0XF 01F jHhf jJXF1F i
¼ dF 01F1fhXðCoÞ þ hXDðCoÞ½JðJ þ 1Þ þ J 0ðJ 0 þ 1Þ�=2g
� ð�1ÞJ0þI1þF1
I1 J 0 F1J I1 1
( )ð�1ÞJ
0�X J 0 1 J
�X 0 X
!
� ½ð2J 0 þ 1Þð2J þ 1ÞI1ðI1 þ 1Þð2I1 þ 1Þ�1=2
þ dF 01F1
eQqðCoÞ4
ð�1ÞJ0þI1þF1
I1 J 0 F1J I1 2
( )ð�1ÞJ
0�X
�J 0 2 J
�X 0 X
!
� ð2J 0 þ 1Þð2J þ 1ÞðI1 þ 1Þð2I1 þ 1Þð2I1 þ 3ÞI1ðI1 � 1Þ
� �1=2
þ hXðFÞð�1ÞJþ2F 01þI1þI2þFþ1 I2 F 0
1 F
F1 I2 1
( )
�I1 J 0 F 0
1
1 F1 J
( )ð�1ÞJ
0�X J 0 1 J
�X 0 X
!
� ½ð2F 01 þ 1Þð2F1 þ 1Þð2J 0 þ 1Þð2J þ 1ÞI2ðI2 þ 1Þ
� ð2I2 þ 1Þ�1=2; ð3Þ
where I1 and I2 are nuclear spin quantum numbers of
cobalt(ICo ¼ 7=2) and fluorine(IF ¼ 1=2), respectively.
The molecular constants were determined by a least-
squares calculation. The standard deviation of the fitwas 29 kHz. The molecular constants determined are
listed in the second column of Table 1. The third column
T. Okabayashi, M. Tanimoto / Journal of Molecular Spectroscopy 221 (2003) 149–155 151
lists the constants reported by Ram et al. [6]. Therotational and centrifugal constants determined in
the present work well agree with those obtained from
the near infrared electronic transitions. The observed
and calculated transition frequencies are summarized
with their residuals in Table 2.
Table 2
Observed transition frequencies of CoF (X 3U4) in MHz
J 0–J F 01–F1 F 0–F Obs. Freq. O
11–10 7.5–6.5 7–6 256026.669
8.5–7.5 8–7 256009.764 )9.5–8.5 9–8 255987.677 )10.5–9.5 10–9 255960.165
11.5–10.5 11–10 255927.094 )12.5–11.5 12–11 255888.529 )13.5–12.5 13–12 255844.415 )14.5–13.5 14–13 255794.775 )
12–11 8.5–7.5 8–7
9.5–8.5 9–8 279235.919 )10.5–9.5 10–9 279216.544 )11.5–10.5 11–10 279192.964 )12.5–11.5 12–11 279165.144 )13.5–12.5 13–12 279133.059 )14.5–13.5 14–13 279096.775
15.5–14.5 15–14 279056.166
13–12 9.5–8.5 9–8 302476.571 )10.5–9.5 10–9 302462.624
11.5–10.5 11–10 302445.464
12.5–11.5 12–11 302424.965 )13.5–12.5 13–12 302401.231 )14.5–13.5 14–13 302374.130 )15.5–14.5 15–14 302343.673 )16.5–15.5 16–15 302309.873
14–13 10.5–9.5 10–9 325700.673
11.5–10.5 11–10 325687.849 )12.5–11.5 12–11 325672.640
13.5–12.5 13–12 325654.746
14.5–13.5 14–13 325634.198
15.5–14.5 15–14 325611.028
16.5–15.5 16–15 325585.083
17.5–16.5 17–16 325556.462
16–15 12.5–11.5 12–11 372140.053
13.5–12.5 13–12 372129.458
14.5–13.5 14–13 372117.094 )15.5–14.5 15–14 372103.048
16.5–15.5 16–15 372087.144 )17.5–16.5 17–16 372069.509
18.5–17.5 18–17 372050.024 )19.5–18.5 19–18 372028.770
17–16 13.5–12.5 13–12 395353.571 )14.5–13.5 14–13 395343.844
15.5–14.5 15–14 395332.632 )16.5–15.5 16–15 395320.023
17.5–16.5 17–16 395305.886 )18.5–17.5 18–17 395290.292 )19.5–18.5 19–18 395273.177
20.5–19.5 20–19 395254.504 )aObserved minus calculated frequency.b Excluded from the fit.
4. Results and discussion
Hyperfine splittings arising from the nuclear spins of
both cobalt and fluorine were observed in the present
experiment. The hyperfine parameters of Frosch and
Foley [14], a, bF and c, are represented as
)Ca F 0–F Obs. Freq. O)Ca
0.003 8–7 256019.667 0.009
0.004 9–8 256003.812 )0.0350.010 10–9 255981.954 )0.112b
0.001 11–10 255954.489 0.023
0.026 12–11 255921.147 0.012
0.010 13–12 255882.176 0.037
0.009 14–13 255837.539 0.012
0.016 15–14 255787.354 0.011
9–8
0.044 10–9
0.020 11–10 279211.557 0.032
0.018 12–11 279187.987 0.073
0.019 13–12 279159.898 )0.0120.028 14–13 279127.521 )0.0290.027 15–14 279090.809 )0.0520.020 16–15 279049.803 )0.059
0.011 10–9 302471.372 0.000
0.008 11–10 302457.952 0.018
0.004 12–11 302440.972 0.009
0.054 13–12 302420.552 0.035
0.024 14–13
0.016 15–14 302369.305 )0.0150.009 16–15 302338.599 )0.0020.021 17–16 302304.448 )0.031
0.053 11–10 325696.130 0.053
0.059 12–11
0.006 13–12 325668.594 )0.0280.011 14–13 325650.728 0.000
0.019 15–14 325630.094 0.006
0.079 16–15 325606.719 0.008
0.056 17–16 325580.619 0.018
0.061 18–17
0.005 13–12 372136.472 )0.0470.025 14–13 372126.040 )0.083b
0.004 15–14 372113.853 )0.0270.037 16–15 372099.810 0.004
0.007 17–16 372083.794 )0.108b
0.011 18–17 372066.151 )0.0160.012 19–18 372046.583 )0.0120.022 20–19 372025.133 )0.043
0.010 14–13 395350.452 0.012
0.009 15–14 395340.841 )0.0220.024 16–15 395329.777 0.019
0.004 17–16 395317.131 )0.0030.018 18–17 395302.984 )0.0040.004 19–18 395287.336 0.020
0.001 20–19 395270.124 0.014
0.024 21–20 395251.358 0.000
� �152 T. Okabayashi, M. Tanimoto / Journal of Molecular Spectroscopy 221 (2003) 149–155
a ¼ 2lBgNlN1
K
Xi
li1
r3i o
; ð4Þ
bF ¼ 8p3gslBgNlN
1
n
Xi
hjWð0Þij2is; ð5Þ
and
c ¼ 3
2gslBgNlN
1
n
Xi
3 cos2 hi � 1
r3i
� �s
: ð6Þ
In the present study, however, we could not determine
the Frosch and Foley hyperfine parameters separately
because the transitions were observed only in the X ¼ 4
substate without X ¼ 3 and X ¼ 2 substates. Instead of
these three parameters, an effective magnetic hyperfine
constant h4 ¼ 3aþ bþ c was determined in the present
analysis, where hX ¼ aKþ ðbþ cÞR and b ¼ bF � c=3.The centrifugal distortion term h4D for the cobalt
hyperfine constant was needed to reproduce the ob-
served transition frequencies, but that for fluorine was
not necessary. Nevertheless, the h4D(Co) value seems to
be effectively determined because jh4DðCoÞ=h4ðCoÞj ’10�4 is much larger than D=B ’ 10�6. The apparently
large centrifugal distortion of hyperfine h parameter
often arises when a case (a) multiplet state is modeledusing a case (c) approach, or when the full spin–orbit
manifold cannot be observed. For example, this prob-
lem was found in the B4P state of the vanadium oxide
VO radical. The large hXD value of VO in the B4P(v ¼ 1) state found in the case (c) analysis was accounted
for as a second order cross term between the spin un-
coupling and Fermi contact operators in the case (a)
Hamiltonian [15]. In the later work, the analysis usingthe full case (a) Hamiltonian on a large data set for the
v ¼ 0 level did not need the hXD term any more [16].
In the case (a) Hamiltonian, the magnetic hyperfine
interaction is presented in [17].
hK0SR0J 0X0I jjHhf jjKSRJXIi¼ ½IðI þ 1Þð2I þ 1Þð2J 0 þ 1Þð2J þ 1Þ�1=2
� dKK0Xq
ð(
� 1ÞJ0�X0 J 0 1 J
�X0 q X
!
� aKdRR0dXX0
"þ bF ð � 1ÞS�R0 S 1 S
�R0 q R
� �
� ½SðS þ 1Þð2S þ 1Þ�1=2 þffiffiffiffiffi30
p
3cð � 1Þqð � 1ÞS�R0
�S 1 S
�R0 q R
� �1 2 1
�q 0 q
� �½SðS þ 1Þð2S þ 1Þ�1=2
#
þ dXq¼�1
dK0K�2ð � 1ÞJ0�X0
ð � 1ÞS�R0 J 0 1 J
�X0 q X
!
�S 1 S
�R0 q R
� �½SðS þ 1Þð2S þ 1Þ�1=2
): ð7Þ
Using this equation, the diagonal matrix element of3U4 and the off-diagonal elements between 3U4 � 3U3
are expressed by the following equations:
h3U4; JIF jHhf j3U4; JIF i ¼ 4 3a�
þ bF þ 2
3c�X ðJIF Þ
¼ 4h4X ðJIF Þ; ð8Þ
and
h3U4; JIF jHhf j3U3; JIF i ¼ bF
�� 1
3c�X ðJIF Þ
� ½2ðJðJ þ 1Þ � 12Þ�1=2
¼ bX ðJIF Þ½2ðJðJ þ 1Þ � 12Þ�1=2;ð9Þ
where X ðJIF Þ is an expression including several quan-
tum numbers as J , F , and I . With a spin-uncoupling
term included in the case (a) 3U matrix elements [22],
this off-diagonal element is approximately rewritten as
follows:
h3U4; JIF jH j3U3; JIF i ’ � ½B� bX ðJIF Þ�� ½2ðJðJ þ 1Þ � 12Þ�1=2: ð10Þ
Based on a second-order perturbation theory, the 3U4
energy is corrected by
DEð2Þ ’ 2ðJðJ þ 1Þ � 12ÞDEð3U4 � 3U3Þ
ðB2 � 2bBX ðJIF Þ þ b2X ðJIF Þ2Þ:
ð11ÞBy comparing Eq. (8) with Eq. (11), the second term in
Eq. (11) can be identified with the h4D term:
h4D ’ � bBDEð3U4 � 3U3Þ
’ � bB3A
: ð12Þ
Using the h4D(Co) and B0 values in Table 1 and
A ¼ �232:87 cm�1 [4], the off-diagonal b(Co) term is
estimated to be )302MHz. Although this value is not
very accurate, its absolute value is roughly close to that
of CoH (136MHz) [22]. This finding supports the as-
sumption that the present h4D(Co) value is an apparenteffective parameter arising when a case (a) multiplet
state is modeled using a case (c) coupling.
Electronic configuration of CoF has been proposed
as (core)ð9rÞ2ð1dÞ3ð4pÞ3 in [3], and the unpaired elec-
trons belong to the 1d and 4p orbitals. The 1d orbital is
constructed solely from a 3d(Co) orbital. On the other
hand, the 4p orbital is mainly constructed from a 3d(Co)orbital but includes small amounts of 4p(Co) and 2p(F)orbitals. Thus, the hyperfine constant h4(Co) reveals thecontributions of the 3d(Co) orbitals to the partially filled
1d and 4p orbitals. On the other hand, h4(F) representsthe contribution of the 2p(F) orbitals to the 4p orbital of
an unpaired electron.
If h1=r3io in Eq. (4) is approximately equal to h1=r3isin Eq. (6), a(F) and c(F) constants are related to a
T. Okabayashi, M. Tanimoto / Journal of Molecular Spectroscopy 221 (2003) 149–155 153
unique atomic constant P ðFÞ ¼ 4400MHz listed in [18].Since the 4p orbital does not include the contribution of
the 2s orbital of the fluorine, the bF (F) constant shouldbe close to zero. The a(F) and c(F) constants are thus
simplified to the following approximate equations:
aðFÞ ¼ 2lBgNlN1
32
1
r3
� �1d
�þ 1
r3
� �4p
�
¼ cF4p3
2lBgNlN1
r3
� �2ppðFÞ
" #
’ cF4p3
P ðFÞ; ð13Þ
and
cðFÞ ¼ 3
2gslBgNlN
1
2
3 cos2 h� 1
r3
� �1d
�
þ 3 cos2 h� 1
r3
� �4p
�
¼ 3cF4p4
gslBgNlN3 cos2 h� 1
r3
� �2ppðFÞ
" #
’ � 3cF4p10
PðFÞ; ð14Þ
where cF4p represents the contribution of the 2p(F) orbitalto the 4p orbital and the angular factor h3 cos2 h� 1i2ppis taken to be )2/5 [18]. The h4(F) value is derived as
follows:
h4ðFÞ ¼ 3aðFÞ þ bF ðFÞ þ2
3cðFÞ ¼ 4cF4p
5PðFÞ: ð15Þ
In order to reproduce the observed value h4ðFÞ ¼ 234MHz, we obtained cF4p ¼ 0:066. This value is consistent
with the prediction that the 4p orbital is dominantly
(’93%) constructed from the 3d(Co) atomic orbital.
This finding means that the fluorine atom almost exists
as the closed shell F� ion and hardly possesses an
unpaired electron.
There are only scarce reports on hyperfine constants
for metal monofluoride radicals bearing unpaired elec-trons, except for alkaline earth fluorides like CaF [19]
and iron fluoride FeF [20]. Electronic configurations of
CaF and FeF are represented as (core)ð9rÞ1 and
(core)ð9rÞ1ð1dÞ3ð4pÞ2ð10rÞ1, respectively. The hyperfine
constant c(F) for CaF is represented as
cðFÞ ¼ 3
2gslBgNlN
3 cos2 h� 1
r3
� �9r
� �
¼ 3cF9r2
gslBgNlN3 cos2 h� 1
r3
� �2prðFÞ
" #
’ 6cF9r5
PðFÞ; ð16Þ
where cF9r represents the contribution of the 2p(F) orbitalto the 9r orbital and the angular factor h3 cos2 h� 1i2pr
is taken to be 4/5 [18]. To reproduce the experimentalvalue 41.2MHz [19], cF9r is obtained to be 0.008. Al-
though the cF9r value for CaF should not directly be
compared to the cF4p value for CoF (0.066), an ionic
molecule has qualitatively smaller orbital overlap be-
tween two bonding atoms than a covalent molecule.
Thus, the small value of cF9r probably reflects that CaF is
more ionic than CoF.
The similar expression can be given for FeF,
cðFÞ ¼ 3
2gslBgNlN
1
5
3cos2 h� 1
r3
� �9r
�
þ 3cos2 h� 1
r3
� �1d
þ 23cos2 h� 1
r3
� �4p
þ 3cos2 h� 1
r3
� �10r
�
¼ 3cF4p10
gslBgNlN cF9r3cos2 h� 1
r3
� �2prðFÞ
"
þ 2cF4p3cos2 h� 1
r3
� �2ppðFÞ
þ cF10r3cos2 h� 1
r3
� �2prðFÞ
#
’ 6
25cF9r�
� cF4p þ cF10rPðFÞ: ð17Þ
If cF9r ’ cF4p ’ cF10r can be assumed, an averaged cF
value for FeF is obtained to be 0.049 to reproduce the
experimental value 51.7MHz [20]. This value is in rough
agreement with the cF4p value of CoF (0.066), and FeFseems qualitatively as ionic as CoF.
It is notoriously difficult to estimate the molecular
hyperfine parameters from the atomic values for metal
containing molecules without a high-quality ab initio
work, because the molecular states are by no means
simply related to atomic states. However, we dare to
estimate the hyperfine constants a(Co), bF (Co) and
c(Co) from the hyperfine constants ajk3d of atomic cobalt[21] using a similar procedure.
aðCoÞ ¼ 2lBgNlN1
32
1
r3
� �1d
�þ 1
r3
� �4p
�
¼ 2þ cCo4p3
2lBgNlN1
r3
� �3dðCoÞ
" #
’ 2þ cCo4p3
� �a013d ; ð18Þ
bF ðCoÞ ¼8p3gslBgNlN
1
2½hjWð0Þj2i1d þ hjWð0Þj2i4p�
¼ 8p3gslBgNlN
1
2½hjWð0Þj2i3ddðCoÞ
þ cCo4p hjWð0Þj2i3dpðCoÞ�
’ 1þ cCo4p2
� �a103d ; ð19Þ
and
154 T. Okabayashi, M. Tanimoto / Journal of Molecular Spectroscopy 221 (2003) 149–155
cðCoÞ ¼ 3
2gslBgNlN
1
2
3 cos2 h� 1
r3
� �1d
�
þ 3 cos2 h� 1
r3
� �4p
�
¼ 3
4gslBgNlN
3 cos2 h� 1
r3
� �3ddðCoÞ
"
þ cCo4p3 cos2 h� 1
r3
� �3dpðCoÞ
#
’�� 3ð2� cCo4p Þ
14
�a123d ; ð20Þ
where cCo4p is the contribution of the 3d(Co) orbital to the
4p orbital and the contribution of 4p(Co) is neglected.The angular factors h3 cos2 h� 1i3dd and h3 cos2 h� 1i3dpare assumed to be )4/7 and 2/7, respectively [18]. If
a01ð3d;3d84sÞ ¼ 617:9, a10ð3d;3d74s2Þ ¼ �69:4, a12ð3d;3d84sÞ ¼ 857:1MHz [21], and cCo4p ¼ 1� cF4p ¼ 0:934 are used, we
predict the hyperfine constants as aðCoÞ ¼ 604,
bF ðCoÞ ¼ �67, and cðCoÞ ¼ �196MHz. Using an
equation like Eq. (15), the h4(Co) value is calculated to
be 1614MHz. This value is quite different from theobserved value, 975MHz. If cCo4p is adjusted so as to
reproduce the observed value, cCo4p is obtained to be al-
most zero: this result means that the unpaired 4p orbital
is almost purely constructed from the 2p orbital of
fluorine and it is inconsistent with the fact that CoF is a
highly ionic species represented as CoþF�. Probably, the
valence orbitals of the CoF molecule are strongly de-
formed from the atomic cobalt 3d orbitals, and it seemsunsuitable to use the atomic hyperfine parameters of
cobalt for estimation of those of the CoF molecule.
Interestingly, the h4(Co) values of the CoH [22] and
CoCl [23] molecules are reported to be 1543 and
1318MHz, respectively. They are much closer to the
present estimated value 1614MHz. Since CoH and CoCl
as well as CoF seem to have the ionic structure repre-
sented as CoþX�, the similar procedure for hyperfineanalysis can be applied with small cCo4p values. Judging
from the observed h4(Co) value matching with the esti-
mated one, the orbitals of CoH and CoCl seem to be
better-behaving than those of CoF.
For the CoH molecule, experimental hyperfine
constants have also been reported as aðCoÞ ¼ 621,
bF ðCoÞ ¼ �16, and cðCoÞ ¼ �456MHz [22]. Although
a(Co) constant is in good agreement with the estimatedones, the experimental c(Co) value of CoH is not close
to the present estimation. One of the possible explana-
tions is that the angular factors h3 cos2 h� 1i in Eq. (20)
are quite different from the ideal case by the orbital
deformation caused by Co–H bonding. If this estimation
is true, it is likely that the a(Co) parameters of CoF and
CoH will have similar values each other. Indeed, an-
other ionic cobalt compound CoO (X 4Di) also has a
similar a(Co) value, 649MHz [24]. Using a(Co) of CoH,bF (Co) and c(Co) of CoF are estimated to be )497 and
)586MHz, respectively, to reproduce h4ðCoÞ ¼ 975 and
bðCoÞ ¼ �302MHz. The obtained c(Co) value is con-
sistent to that of CoH, )456MHz. On the other hand,
the obtained bF (Co) value is of anomalously large neg-
ative value, but it is not too large in consideration of
that of CoO, )183MHz. As mentioned above, however,
the present b(Co) value is too crude to derive accuratehyperfine parameters of Frosch and Foley. The obser-
vation of hyperfine splittings in other spin substates 3U3
and 3U2 is needed for further detailed discussion.
The electric quadrupole coupling constant eQq(Co) isobtained to be )77.50(91)MHz, which agrees with that
of CoH ()92.5(47)MHz [22]) within their three standard
deviations. This similarity means that the electric charge
distribution around the Co nucleus of CoF is quantita-tively similar to that of CoH. Another ionic cobalt
compound CoO (X 4Di) also has a negative eQq(Co)value )38MHz [24], but a more covalent species CoC
(X 2Rþ) has a large positive value, 303MHz [25]. Since
the eQq constant is affected by the distributions of core-
as well as valence-electrons, it is difficult to discuss the
constants quantitatively without a high-level ab initio
calculation when the orbital polarization is striking. Tounderstand these cobalt hyperfine constants including
eQq(Co) is a good subject of current theoretical calcu-
lations.
Acknowledgments
The research was supported by Japan Society for thePromotion of Science through Grant-in-Aid for Scien-
tific Research (No. 12740316). T.O. thanks the Kawa-
saki Steel 21st Century Foundation for financial
support. T.O. also acknowledges financial support from
the Hamamatsu Foundation for Science and Technol-
ogy Promotion.
References
[1] K.P. Huber, G. Herzberg, Molecular Spectra and Molecular
Structure. IV. Constants of Diatomic Molecules, Van Nostrand
Reinhold, New York, 1979.
[2] A.J. Merer, Annu. Rev. Phys. Chem. 40 (1989) 407–438.
[3] A.G. Adam, L.P. Fraser, W.D. Hamilton, M.C. Steeves, Chem.
Phys. Lett. 230 (1994) 82–86.
[4] A.G. Adam, W.D. Hamilton, J. Mol. Spectrosc. 206 (2001)
139–142.
[5] R.S. Ram, P.F. Bernath, S.P. Davis, J. Mol. Spectrosc. 173 (1995)
158–176.
[6] R.S. Ram, P.F. Bernath, S.P. Davis, J. Chem. Phys. 104 (1996)
6949–6955.
[7] T. Okabayashi, M. Tanimoto, J. Chem. Phys. 105 (1996) 7421–
7424.
T. Okabayashi, M. Tanimoto / Journal of Molecular Spectroscopy 221 (2003) 149–155 155
[8] M. Tanimoto, S. Saito, T. Okabayashi, Chem. Phys. Lett. 242
(1995) 153–156.
[9] M. Tanimoto, T. Sakamaki, T. Okabayashi, J. Mol. Spectrosc.
207 (2001) 66–69.
[10] T. Okabayashi, E. Yamazaki, T. Honda, M. Tanimoto, J. Mol.
Spectrosc. 208 (2001) 66–70.
[11] T. Okabayashi, M. Tanimoto, J. Chem. Phys. 99 (1993) 3268–
3270.
[12] E. Hirota, High-Resolution Spectroscopy of Transient Molecules,
Springer, Berlin, 1985.
[13] S. Yamamoto, S. Saito, J. Chem. Phys. 86 (1987) 102–105.
[14] R.A. Frosch, H.M. Foley, Phys. Rev. 88 (1952) 1337–1349.
[15] G. Huang, A.J. Merer, D.J. Clouthier, J. Mol. Spectrosc. 153
(1992) 32–40.
[16] A.G. Adam, M. Barnes, B. Berno, R.D. Bower, A.J. Merer, J.
Mol. Spectrosc. 170 (1995) 94–130.
[17] J.M. Brown, M. Kaise, C.M.L. Kerr, D.J. Milton, Mol. Phys. 36
(1978) 553–582.
[18] J.R. Morton, K.F. Preston, J. Mag. Reson. 30 (1978) 577–582.
[19] W.J. Childs, G.L. Goodman, L.S. Goodman, J. Mol. Spectrosc.
86 (1981) 365–392.
[20] M.D. Allen, L.M. Ziurys, J. Chem. Phys. 106 (1997) 3494–
3503.
[21] G.H. Guth€oohrlein, H.P. Keller, Z. Phys. D 17 (1990) 181–
193.
[22] S.P. Beaton, K.M. Evenson, J.M. Brown, J. Mol. Spectrosc. 164
(1994) 395–415.
[23] A.G. Adam, J.R.D. Peers, Y. Teng, C. Linton, J. Mol. Spectrosc.
212 (2002) 111–117.
[24] K.C. Namiki, S. Saito, J. Chem. Phys. 114 (2001) 9390–9394.
[25] M.A. Brewster, L.M. Ziurys, Astrophys. J. 559 (2001) L163–
L166.
Top Related