The rotational spectrum of the CrF radical in the X6∑+ state

Article abstract of DOI:10.1063/1.472608

The rotational spectrum of the CrF radical in the X⁶∑⁺ state was observed by employing a source modulation microwave spectrometer. The CrF radical was generated in a free space cell by a dc glow discharge in CF₄ and He. The chromium atom was supplied by the sputtering reaction from chromium powder placed over a lower surface of the cylindrical electrodes. The transitions with N=12-11 to 20-19 were measured in the region between 270 and 460 GHz. The rotational, centrifugal distortion and several fine-structure constants were obtained by a least squares analysis.

Full text of DOI:10.1063/1.472608

The rotational spectrum of the CrF radical in the X 6Σ+ state
Toshiaki Okabayashi and Mitsutoshi Tanimoto
Citation: The Journal of Chemical Physics 105, 7421 (1996); doi: 10.1063/1.472608
View online: http://dx.doi.org/10.1063/1.472608
View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/105/17?ver=pdfcov
Published by the AIP Publishing
Articles you may be interested in
Microwave spectroscopy of mixed alkali halide dimers: LiNaF2
J. Chem. Phys. 105, 9754 (1996); 10.1063/1.472831
Microwave spectroscopy of the HCCS and DCCS radicals (X̃ 2Π i ) in excited vibronic states: A study of the
Renner–Teller effect
J. Chem. Phys. 105, 8020 (1996); 10.1063/1.472715
Laserrf double resonance spectroscopy of 174YbF in the X 2Σ+ state: Spinrotation, hyperfine interactions, and
the electric dipole moment
J. Chem. Phys. 105, 7412 (1996); 10.1063/1.472569
Microwave spectrum of the FS2 radical in the ground electronic X̃2 A″ state
J. Chem. Phys. 104, 7437 (1996); 10.1063/1.471652
Statespecific collision dynamics of OH radicals and N atoms
AIP Conf. Proc. 146, 545 (1986); 10.1063/1.35955
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:
209.183.185.254 On: Sat, 29 Nov 2014 21:55:22

6
The rotational spectrum of the CrF radical in the X ⌺؉ state
Toshiaki Okabayashi and Mitsutoshi Tanimoto
Department of Chemistry, Faculty of Science, Shizuoka University, 836 Oya, Shizuoka 422, Japan
͑Received 21 June 1996; accepted 24 July 1996͒
6
The rotational spectrum of the CrF radical in the X ⌺ϩ state was observed by employing a source
modulation microwave spectrometer. The CrF radical was generated in a free space cell by a dc
glow discharge in CF4 and He. The chromium atom was supplied by the sputtering reaction from
chromium powder placed over a lower surface of the cylindrical electrodes. The transitions with
Nϭ12Ϫ11 to 20Ϫ19 were measured in the region between 270 and 460 GHz. The rotational,
centrifugal distortion and several fine-structure constants were obtained by a least squares analysis.
© 1996 American Institute of Physics. ͓S0021-9606͑96͒01341-4͔
I. INTRODUCTION
submillimeter wave spectroscopy of the CrF radical gener-
ated by the sputtering reaction.
Transition metal compounds have often high electron-
orbital and electron-spin angular momenta due to their
d-electrons. The d-electrons thus cause a lot of low lying
electronic excited states. These electronic states and their
substrates result in remarkably complex spectra observed by
a high resolution spectroscopic method. It is quite compli-
cated to analyze them and to understand their spectroscopic
meaning. Since it is also difficult to efficiently produce the
transition metal compounds in the gas phase, the electronic
spectra measured with a high sensitivity spectrometer have
been mainly employed to study such species. Moreover,
most of the works have been carried out for hydrides and
oxides, and a few works have been reported for other species
like halides, nitrides, carbides, etc.
II. EXPERIMENT
The present experiment was carried out using source
modulated microwave spectrometers at Shizuoka
University12 and at the Institute for Molecular Science.13
Millimeter and submillimeter wave radiation was generated
by multiplying the output of a klystron. The radiation trans-
mitted through a free space cell was detected by an InSb
detector cooled at 4.2 K by liquid helium. The cell contained
a pair of cylindrical electrodes for a dc glow discharge. The
cell was surrounded by Helmholtz coils in order to cancel the
magnetic field of the earth.
The diatomic transition metal halides MX ͑Mϭtransition
metal; XϭF, Cl, Br, and I͒ are highly ionic species repre-
sented as MϩXϪ. All unpaired electrons mainly exist on the
metal atom because of the closed shell structure of the XϪ
ion. Thus their electronic states strongly reflect the character
of metallic ions Mϩ. It is interesting to compare electronic
structures of MF, MCl, MBr, and MI, but there are only few
The CrF radical was generated in the free space cell by a
dc glow discharge in CF4 and He. The chromium atom was
supplied by the sputtering reaction from chromium powder
scattered on the lower surface of the electrodes. The transi-
tion frequencies were predicted from molecular constants re-
cently obtained by electronic spectra.4,5 First we searched for
the N(J)ϭ16(37/2)Ϫ15(35/2) transition near 364.5 GHz. A
weak line which showed remarkably paramagnetic character
was observed at 364542 MHz. The line appeared when the
cell temperature was below Ϫ150 °C and discharge current
was above 400 mA. With cooler cell temperature and higher
discharge current, the line was stronger. Accordingly the cell
was cooled to the liquid nitrogen temperature and the dis-
charge current was set to about 700 mA ͑maximum output of
our power supply͒. Removal of CF4 or He from the system
made the line disappear. Optimum sample pressure was 5
mTorr of CF4 and 40 mTorr of He. When chromium powder
was taken away from the cell, the line was still observed but
somewhat weaker. This was explained by implying that
chromium atom was also supplied from the stainless steel
electrodes as in the case of the CrCl radical,9,10 for the stain-
less steel contains about 20% of chromium. Since we could
detect other five spin components within 50 MHz differences
from predicted frequencies, we identified this species as the
CrF radical. Finally we observed 43 lines from Nϭ12Ϫ11 to
20Ϫ19 transitions in the region between 270 and 460 GHz.
Figure 1 shows an example of the observed spectral line.
1
works for them except the ⌺ϩ species like CuX and AgX.
Chromium monohalides ͑CrX͒ are the species that have
scarcely been studied by any spectroscopic methods. Re-
cently the electronic spectra of CrF, however, have been
studied by several groups. The first reliable spectrum was
6
6
reported by Dubov et al., who observed the A ⌺ϩ –X ⌺ϩ
transition with high resolution and carried out the rotational
analysis.1,2 Devore et al.3 studied chemiluminescence and
obtained low-resolution spectra on several electronic bands.
Launila and his associates4,5 reported high resolution Fourier
transform spectrum of the A6⌺ϩ –X6⌺ϩ and B6⌸–X6⌺ϩ
bands.
Very few millimeter and submillimeter wave spectro-
scopic studies have been carried out for some transition
metal multiplet radicals such as FeO(5⌬i)6 and FeS(5⌬i).7
Quite lately, we have observed FeCl(6⌬i)8 and CrCl
(6⌺ϩ),9,10 and Namiki and Saito have studied NiO(3⌺Ϫ).11
These species were efficiently generated by the sputtering
reaction of electrodes or metallic compounds placed on the
electrodes. In the present paper, we report millimeter and
J. Chem. Phys. 105 (17), 1 November 1996
0021-9606/96/105(17)/7421/4/$10.00
© 1996 American Institute of Physics
7421
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:
209.183.185.254 On: Sat, 29 Nov 2014 21:55:22

7422
T. Okabayashi and M. Tanimoto: Rotational spectrum of CrF
III. ANALYSIS
distortion, Hss spin-spin interaction, and Hsr spin-rotation in-
teraction. In order to fit the data within experimental error,
two extra higher order terms which do not appear in the
electronic states of triplet or lower multiplicity are needed:
the third order spin-rotation term ␥S and the fourth order
spin-orbit term ␪. They are represented in case ͑b͒ basis
functions as follows:14,15
The observed transition frequencies were analyzed by a
6
least squares analysis using a
⌺ case ͑b͒ effective
Hamiltonian.10 The Hamiltonian employed is
HeffϭHrotϩHssϩHsr ,
͑1͒
where Hrot represents rotational energy including centrifugal
J
S
N
2
1
3
ͱ70
4ͱ6
Ј
͑3͒
NϩSϩJϩ1
NϩN
Ј
N ⌳ SJ MЈ
Ј Ј
͉
Hsr
͉
N⌳SJMJ ϭ␦
␦
␥ Ϫ͒
͑
S
Ϫ͒
͑
Ј
͗
͘
ͭ
ͮ
ͭ
ͮ
J J
M
M
J
Ј
Ј
J
J
3
N
S
N
N
N
Ј
N
2
0
N
Ј
1/2
N Ϫ⌳
1/2
Ј
ϫ
2N ϩ1͒ 2Nϩ1͒
Ϫ͒
N Nϩ1͒ 2Nϩ1͒
͓͑
͓͑
͑
͔
͑
͓ ͑
͑
͔
Ј
ͩ
ͪ
Ϫ⌳
⌳
1/2
ϫ
2SϪ2͒ 2SϪ1͒ 2S͒ 2Sϩ1͒ 2Sϩ2͒ 2Sϩ3͒ 2Sϩ4͒
,
͑2͒
͑3͒
͑
͑
͑
͑
͑
͑
͔
and
J
S
N
N
4
0
N
Ј
Ј
␪
͑4͒
NϩSϩJ
N Ϫ⌳
1/2
Ј
Ј
N ⌳ SJ MЈ
Ј Ј
͉
Hso
͉
N⌳SJMJ ϭ␦
␦
Ϫ͒
Ϫ͒
2N ϩ1͒ 2Nϩ1͒
͓͑ ͑ ͔
Ј
͑
͑
Ј
͗
͘
ͩ
ͪ
ͭ
ͮ
J J
M M
Ј
J
J
J
Ј
24
4
N
S
Ϫ⌳
⌳
1/2
ϫ
2SϪ3͒ 2SϪ2͒ 2SϪ1͒ 2S͒ 2Sϩ1͒ 2Sϩ2͒ 2Sϩ3͒ 2Sϩ4͒ 2Sϩ5͒
.
͔
͓͑
͑
͑
͑
͑
͑
͑
͑
͑
The molecular constants were determined by a least squares
calculation. As in Ref. 15, the basis set was truncated in the
calculations at ⌬NϭϮ4 without loss in accuracy. The stan-
dard deviation of the fit was about 20 kHz. The molecular
constants determined are listed in the leftmost column of
Table I. Table I also lists the constants reported by Wallin
et al.5 in the rightmost column.
The fine structure constants determined in the present
work well agree with those obtained from the near infrared
electronic transition, but the rotational and centrifugal distor-
tion constants not perfectly within three times of their stan-
dard deviations. These disagreements seem to be caused by
high-J-biased data in the electronic transition measurements.
In Ref. 4, Launila published more than 3000 of transition
wavenumbers observed between Jϭ5.5 and Jϭ120.5 re-
gion. Since these observed data contain a lot of high-J tran-
sitions around Jϭ100, it is essential to include the contribu-
tion of a J ͑or N) dependent higher-order term, especially the
sextic centrifugal distortion constant H0.
In order to determine molecular constants more accu-
rately, the least squares calculation was simultaneously car-
ried out for the combined microwave and near infrared data.
6
About 1600 of combination differences in the X ⌺ϩ state
derived from Ref. 4 and 43 of our microwave data led to the
constants in the central column of Table I. Observed micro-
wave frequencies and the residuals of the combined fit are
summarized in Table II. The sextic centrifugal distortion
⌺
ϩ).a
6
TABLE I. Molecular constants of CrF ͑X
MW
MWϩNIR
NIRb
B0
D0
H0
␭
11369.61615͑56͒
15.05444͑76͒
11369.61433͑34͒
15.04775͑53͒
–7.70͑28͒
16162.4͑12͒
–15.487͑24͒
408.502͑14͒
–0.7555͑95͒
–10.59͑71͒
11370.058͑78͒
15.1741͑57͒
•••
16170.4͑46͒
–18.08͑96͒
408.33͑25͒
Ϫ0.768͑42͒
MHz
kHz
mHz
MHz
kHz
MHz
kHz
kHz
16162.7͑20͒
–15.486͑40͒
408.499͑24͒
–0.754͑16͒
–10.7͑12͒
␭
D
␥
␥
D
␥
S
␪
–5.15͑28͒
–5.12͑17͒
MHz
FIG. 1. The submillimeter wave spectrum of rotational transition of
aValues in parentheses are one standard deviation.
bReference 5. Derived from the equilibrium molecular constants.
6
ϩ
N(J)ϭ20(37/2)Ϫ19(35/2) in the X
⌺
state of the CrF radical. The inte-
gration time was 15 s.
J. Chem. Phys., Vol. 105, No. 17, 1 November 1996
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:
209.183.185.254 On: Sat, 29 Nov 2014 21:55:22

T. Okabayashi and M. Tanimoto: Rotational spectrum of CrF
7423
ϩ).a
6
6
TABLE II. Observed transition frequencies of CrF ͑X
⌺
ϩ) in MHz.
O–Ca
TABLE III. Rotational and fine structural constants of CrX ͑X
CrHb CrFc Cr35Cld
183824.957͑57͒ 11369.61433͑34͒ 5009.34569͑69͒ MHz
⌺
N –N
J –J
Љ
Obs. feq.
Ј
Љ
Ј
B0
␭
12–11
13–12
14–13
15–14
16–15
17–16
18–17
19–18
20–19
19/2–17/2
21/2–19/2
23/2–21/2
25/2–23/2
27/2–25/2
29/2–27/2
272035.593
272543.849
272668.060
272827.737
273162.538
273691.374
0.000
0.242b
0.023
0.047
0.003
6979.79͑17͒
1509.69͑21͒
16162.4͑12͒
408.502͑14͒
7981.0͑25͒
65.646͑26͒
MHz
MHz
␥
͑Ratio͒
␭
␥/B0
0.43
0.23
1.0
1.0
0.49
0.36
Ϫ0.005
aValues in parentheses are one standard deviation.
21/2–19/2
23/2–21/2
25/2–23/2
27/2–25/2
29/2–27/2
31/2–29/2
294690.892
͑295187.527͒
͑295364.547͒
͑295560.796͒
͑295902.048͒
͑296413.974͒
Ϫ0.011
bReference 17.
cThis work.
c
c
c
c
c
dReference 10.
constant H0 was obtained to be Ϫ7.70(28) mHz, and the
values of B0 and D0 slightly decreased from those of micro-
wave results. The fine structure constants did not change
essentially.
23/2–21/2
25/2–23/2
27/2–25/2
29/2–27/2
31/2–29/2
33/2–31/2
͑317356.391͒
͑317842.827͒
͑318059.087͒
͑318284.376͒
͑318631.508͒
͑319129.885͒
c
c
c
c
c
c
IV. DISCUSSION
25/2–23/2
27/2–25/2
29/2–27/2
31/2–29/2
33/2–31/2
35/2–33/2
340026.820
340504.379
340750.682
340999.361
341351.827
341839.182
Ϫ0.033
0.000
0.023
Ϫ0.009
0.016
0.009
The sextic centrifugal distortion constant H in a di-
atomic molecule is given16
2De
2
H0ϷHeϭ
12B Ϫ␻ ␣ ͒
͑
e
e
e
2
3␻
e
27/2–25/2
29/2–27/2
31/2–29/2
33/2–31/2
35/2–33/2
37/2–35/2
362698.906
363168.726
363438.413
363706.313
364063.477
364541.780
Ϫ0.004
0.022
Ϫ0.025
0.005
Ϫ0.026
Ϫ0.013
2 D Ϫ␤ /2͒
͑
0
e
Ӎ
12 B ϩ␣ /2͒2Ϫ␻ ␣ . ͑4͒
͑ ͔
0 e e e
͓
2
3␻
e
Using the values of ␻e , ␣e , and ␤e given in Ref. 5, He is
estimated to be Ϫ7.17 mHz, which is in good agreement
with our H0 value Ϫ7.70(28) mHz. The H0 term is too
small to be determined either only from the near infrared
data or only from the microwave data. Its effect is absorbed
into the rotational and quartic centrifugal distortion con-
stants. For this reason, the values of B0 and D0 of the near
infrared result differ from those of the microwave one. Only
through the combined analysis of both dataset the contribu-
tion of the H0 term could be separated out.
Hyperfine splittings arising from the nuclear spin of
fluorine were not observed in any spectral lines. In the CrF
molecule which is a highly ionic species represented as
CrϩFϪ, five unpaired electrons reside on the chromium
nucleus and the spin density is small on the fluorine nucleus.
Therefore, the hyperfine structure is too small to be observed
in our frequency region.
29/2–27/2
31/2–29/2
33/2–31/2
35/2–33/2
37/2–35/2
39/2–37/2
385370.251
385833.311
386121.545
386405.461
386766.868
387237.561
0.011
Ϫ0.022
Ϫ0.173b
0.006
Ϫ0.024
Ϫ0.061
31/2–29/2
33/2–31/2
35/2–33/2
37/2–35/2
39/2–37/2
41/2–39/2
408039.167
408496.431
408799.886
409096.882
409462.128
409926.494
0.005
Ϫ0.002
0.006
Ϫ0.019
0.013
0.012
33/2–31/2
35/2–33/2
37/2–35/2
39/2–37/2
41/2–39/2
43/2–41/2
430704.414
431156.784
431472.383
431780.586
432149.216
432608.186
0.015
0.191b
0.018
Ϫ0.027
0.020
All unpaired electrons of CrF exist on the Crϩ ion, and
hence the fine structure constants reflect the electronic char-
acter of Cr. CrH and CrCl also seem to be highly ionic spe-
cies like CrF. In Table III, the rotational and fine structure
constants are summarized for CrH,17 CrF, and CrCl.10 The
␭ value of CrF is about twice as large as that of CrH or CrCl.
The ␥/B0 value of CrF is about four and three times greater
than that of CrH and CrCl, respectively. These results imply
that the electronic structure of CrF is quite different from
that of CrH or CrCl.
0.032
35/2–33/2
37/2–35/2
39/2–37/2
41/2–39/2
43/2–41/2
45/2–43/2
453364.949
453812.679
454138.645
454456.467
454828.076
455282.404
0.009
Ϫ0.006
Ϫ0.015
Ϫ0.009
0.010
0.013
aObserved minus calculated frequency from the simultaneous analysis of the
combined microwave and near infrared data.
bDisturbed line. Excluded in the fit.
The spin-spin interaction arises from both a first order
electron spin dipole-dipole interaction and second order spin-
cCalculated frequency.
J. Chem. Phys., Vol. 105, No. 17, 1 November 1996
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:
209.183.185.254 On: Sat, 29 Nov 2014 21:55:22

7424
T. Okabayashi and M. Tanimoto: Rotational spectrum of CrF
orbit interactions with other states.18 In a molecule contain-
ing heavy atoms, the latter is generally larger than the
much stronger when the cell temperature was above
Ϫ150 °C, whereas absorption lines due to CrF appeared be-
low Ϫ150 °C. Although we cannot explain the reason for
this phenomenon, we speculate that reactions on the elec-
trode surface might be sensitively influenced by the tempera-
ture of the electrodes.
6
former. The X ⌺ϩ state is probably represented by the elec-
tronic configuration of Crϩ ͓(4sp␴)1(3d␦)2(3d␲)2͔ XϪ.
This configuration provides nine ⌺ electronic states other
6
4
4
2
than the X ⌺ϩ state; two ⌺ϩ, two ⌺Ϫ, three ⌺ϩ, and
two
⌺
⌺
states. The X ⌺ϩ state interacts with
⌺
and
In our previous work for CrCl,9,10 the temperature of the
cell remarkably affected the production of CrCl. When
AlCl3 was employed as the source of Cl atoms, CrCl was
generated at room temperature. However, when CCl4 or
SiCl4 was used, the cell needed to be cooled down to Ϫ80 or
Ϫ120 °C, respectively, to observe the spectrum of CrCl.
These temperatures are much lower than the melting point of
the precursors: AlCl3 ͑183 °C; sublimation͒, CCl4 ͑Ϫ23 °C͒,
and SiCl4 ͑Ϫ70 °C͒. In the present work for CrF, the opti-
mum cell temperature of Ϫ196 °C ͑liquid nitrogen tempera-
ture͒ is also lower than the melting point of CF4 ͑Ϫ184 °C͒.
Therefore the precursor trapped on the electrodes might play
an important role for the production.
2
Ϫ
6
4
Ϫ
2
Ϫ
states because the spin-orbit selection rules require
18
⌺Ϯϳ⌺ϯ. Since the ⌺Ϫ states probably lie much higher
2
than the ⌺Ϫ states, the ground state mainly interacts with
4
4
Ϫ
the lowest
⌺
state. The coupling constant is thus ex-
pressed using case ͑a͒ basis functions as
Ϫ
3/2
ϩ
3/2
4
6
2
⌺
͉
Hso
͉
⌺
͗
͘
ϩ
5/2
ϩ
3/2
6
6
8␭ϭE
⌺
͒ϪE
⌺
͑
͒ϭ
.
͑5͒
͑
E
4⌺Ϫ͒ϪE 6⌺ϩ͒
͑
͑
The value of the ␭ constant is inversely proportional to the
4
Ϫ
6
energy difference between the excited
⌺
and X ⌺ϩ
states. Ab initio calculation for CrH19 locates the lowest
4
Ϫ
6
⌺
state at 26448 cmϪ1 above the X ⌺ϩ state. If the wave
functions of CrF in the ⌺Ϫ and ⌺ϩ states are similar to
4
6
ACKNOWLEDGMENTS
those of CrH, it is estimated from the ratio of the ␭ values of
4
CrH and CrF that the ⌺Ϫ state of CrF lies at about 11000
The authors are grateful to Professor Shuji Saito of the
Institute for Molecular Science ͑IMS͒ for encouragement and
assistance in the measurement at IMS. The authors also
thank the Ministry of Education, Science and Culture for
support through Grant-in-Aid for Scientific Research ͑Nos.
06228214, 07217209, 07454150, and 07740456͒.
cmϪ1 above the ground state. However, since this estimation
seems to be too crude to apply to a transition-metal-
containing molecule with many low-lying electronic states,
the energy gap estimated above should be regarded as the
lower limit.
The spin-rotation interaction mainly results from the sec-
ond order effects including spin-orbit interaction with ⌸
states as follows:4
1 V. M. Dubov and E. A. Shenyavskaya, Opt. Spectrosc. ͑USSR͒ 62, 195
͑1987͒.
2
´
V. M. Dubov, D. V. Tschechovskoy, E. A. Shenyavskaya, and I. Kovacs,
͉⌸ ⌸͉ ͉⌺
BLϩ
͗͘ ͘
Acta Phys. Hungarica 65, 411 ͑1989͒.
⌺
͉
Hso
E ⌸͒ϪE ⌺͒
͗
3 T. C. Devore, M. McQuaid, and J. L. Gole, High Temp. Sci. 29, 1 ͑1990͒.
4 O. Launila, J. Mol. Spectrosc. 169, 373 ͑1995͒.
5 R. Koivisto, S. Wallin, and O. Launila, J. Mol. Spectrosc. 172, 464
͑1995͒; S. Wallin, R. Koivisto, and O. Launila, J. Chem. Phys. 105, 388
͑1996͒.
␥ϭ4
.
͑6͒
͚
͑
͑
⌸
The contributions from the excited states are proportional to
the rotational constant and inversely proportional to the en-
ergy difference. In the case of the CrX molecule, the ground
state seems to interact mainly with the lowest 6⌸ and/or
6 Y. Endo, S. Saito, and E. Hirota, Astrophys. J. 278, L131 ͑1984͒.
7 S. Takano, Thesis, Nagoya University, 1990.
8 M. Tanimoto, S. Saito, and T. Okabayashi, Chem. Phys. Lett. 242, 153
͑1995͒.
19
6
4⌸ states. Ab initio calculation for CrH suggests the ⌸
and ⌸ states at 11604 and 13718 cmϪ1 above the X ⌺ϩ
4
6
9 T. Oike, T. Okabayashi, and M. Tanimoto, Astrophys. J. 445, L67 ͑1995͒.
10 T. Oike, T. Okabayashi, and M. Tanimoto ͑to be published͒.
11 K. Namiki and S. Saito, Chem. Phys. Lett. 252, 343 ͑1996͒.
12 T. Okabayashi and M. Tanimoto, J. Chem. Phys. 99, 3268 ͑1993͒.
13 S. Saito and M. Goto, Astrophys. J. 410, L53 ͑1993͒.
14 T. Nelis, J. M. Brown, and K. M. Evenson, J. Chem. Phys. 92, 4067
͑1990͒.
6
state, respectively. The corresponding ⌸ state of CrF lies
about 8000 cmϪ1 above the ground state.4,5 If the 6⌸ state is
dominantly interacting with the ground state, ␥/B of CrF is
estimated to be 1.5 times larger than that of CrH because the
energy gap of CrH is about 1.5 times larger than that of CrF.
However, ␥/B of CrF determined experimentally is about
15 S. M. Corkery, J. M. Brown, S. P. Beaton, and K. M. Evenson, J. Mol.
Spectrosc. 149, 257 ͑1991͒.
4
16 W. Gordy and R. L. Cook, Microwave Molecular Spectra, 3rd ed. ͑Wiley,
New York, 1984͒.
four times larger than that of CrH. The ⌸ state, and prob-
ably other states in higher energy region, are also interacting
with the ground state and contributing to this constant.
In the present work, the SiF radical was also found to be
produced by the sputtering reaction. Silicon atom was sup-
plied from the cell made of a pyrex tube. The SiF lines are
17 R. S. Ram, C. N. Jarman, and P. F. Bernath, J. Mol. Spectrosc. 161, 445
͑1993͒.
18 H. Lefebvre-Brion and R. W. Field, Perturbations in the Spectra of Di-
atomic Molecules ͑Academic, Orlando, 1986͒.
19 D. Dai and K. Balasubramanian, J. Mol. Spectrosc. 161, 455 ͑1993͒.
J. Chem. Phys., Vol. 105, No. 17, 1 November 1996
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:
209.183.185.254 On: Sat, 29 Nov 2014 21:55:22