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Infrared diode laser spectroscopy of the ν3 band of the fluoromethyl radical, CH2F
JOURNAL
OF MOLECULAR
SPECTROSCOPY
116, 101-107 (1986)
Infrared Diode Laser Spectroscopy of the v3 Band of the Fluoromethyl Radical, CH2F CHIKASHIYAMADA AND EIZI HIROTA Institutefor MolecularScience, Okazaki444, Japan The v, (C-F stretching) band of the CHrF radical was observed with Doppler-limited resolution, by using infrared diode laser spectroscopy with Zeeman and discharge current modulatjon. The CH,F radical was generated directly in a multiple retkction absorption cefl by the electrical discharge in CH2FCOOCHs. The observed spectrum was analyzed to yield the band origin of 1170.4165(6) cm-’ with one standard error in parentheses, in addition to the rotational constants, centrifugal distortion constants, and spin-rotation interaction constants in the uL)) = 1 state. 0 1986 Academic pnss. Inc.
INTRODUCTION
The planarity of the methyl radical (1) does not subsist anymore when we replace the three hydrogen atoms with fluorine atoms, namely, the CF3 radical has a quite rigid pyramidal structure (2). We then expect that either CHzF or CHF2 or both may exhibit the effect of the inversion in their high-resolution spectra. In a previous paper (3), we have reported the microwave spectrum of CHzF and have shown that the molecule is almost, but not completely, planar. This microwave study was motivated by an infrared diode laser observation of the u3 band, which is described in the present paper. No vibrational spectrum has been reported for CH2F in the gas phase. Jacox and Mill&n (4), Raymond and Andrews (5), and Jacox (6) have identified only the C-F stretching band at 1163 cm-’ in low-temperature matrices. Endo et al. (3) have observed a set of vibrational satellites, which they assigned to the out-of-plane bending or CH2 wagging u4 = 1 state, based upon relative intensity measurements leading to an estimated excitation energy of about 300 cm-’ and upon the observed nuclear spin statistical weight. EXPERIMENTAL
DETAILS
The infrared diode laser spectrometer employed is a Zeeman-modulated spectrometer equipped with a White-type multiple-reflection absorption cell (7). Discharge current modulation described in a previous paper (8) was also used to detect lines with small Zeeman effects. The magnetic field for Zeeman modulation consists of an AC field of 860 Hz with 700 G peak-to-peak superimposed on a DC field of 350 G. Discharge current modulation was combined with conventional source-frequency modulation; the source diode was frequency modulated by a IO-kHz sine wave and the absorption signal, after demodulation by a lock-in amplifier tuned to 10 kHz, was 101
0022-2852186 $3.00 Copyright 0 1986 by Academic Press, Inc. All rights of reproduction in any form rescwcd.
102
YAMADA AND HIROTA
fed to a second lock-in amplifier operated at 150 to 200 Hz, the frequency at which the discharge current was switched on and off. The CHzF radical was found to be most effectively produced by the electrical discharge in methyl fluoroacetate CHPFCOOCHs of 100 mTorr diluted with either Ar or N2 of 400 mTorr. We also tested methyl fluoride as a precursor, as in the microwave study (3), namely, the electrical discharge in a mixture of CHsF and CF, or of CH3F and SF, and the reaction of CHsF with microwave discharge products of CF,, but none of these systems gave spectra of CHlF stronger than those derived from CH2FCOOCH3. In addition, the precursor CHsF exhibited a number of strong lines which interfered with the observation of the CHzF signal. The wavenumbers of CHlF lines were measured using NzO spectral lines (9) as references and a vacuum-spaced confocal etalon (free spectral range of about 0.01 cm-‘) as an interpolation device. OBSERVED SPECTRUM
The wavenumber region from 1139 to 1188 cm-’ was scanned, of which 65% was covered because of mode gaps. Figure 1 shows a part of the observed spectrum around 1170 cm-’ recorded with Zeeman modulation; four Q-branch series are seen. It clearly indicates that odd K, branches are weaker than even K, branches. This observation is consistent with the fact that the vibronic symmetry in the ground state is Bi . No spin-rotation splittings were resolved for Q-branch transitions. Figure 2 shows the K structure of the P(6) transition, The splitting for the K, = 2 line is due to the asymmetry of the molecule, whereas the splittings for the I(, = 3,4, and 5 lines are caused by the spin-rotation interaction. The K, = 0 transition does not appear in Fig. 2, because its Zeeman effect is too small to be used for modulation, and the K, = 1 transitions are located outside the region covered by the diode. Figure 3 compares the P(5) transitions observed by Zeeman modulation and discharge current modulation. It is to be noted that the K, = 1 line appears only in the discharge-currentmodulated spectrum.
qQ3 qQ
7 ?
6
qQ5 ‘O6
7 7
7
4 5
3
4
5
6
I
1169.5 FIG.
6
6 6
1
1170.0
1. Q-branch transitions of the CHzF v3band recorded with Zeeman modulation.
103
DIODE LASER SPECTROSCOPY OF CH2F v3 P(6) Ka
N20 1158.19614cm-’ !
RG. 2. The P(6) transition of the CHIF v3band observed by Zeeman modulation. The middle trace shows an N20 reference line, and the bottom trace represents the fringe pattern generated by a confocal etalon of a free spectral range of about 0.01 cm-‘.
We have assigned 25 Q-branch, 22 P-branch, and 5 R-branch transitions, as listed Table I. All the assigned lines obey u-type selection rules. Several lines are left unassigned, as exemplified by a few lines in Fig. 3. These unassigned lines are probably due to hot band transitions from the o4 = 1 state, but, because the observed data are rather limited, it does not seem to warrant analyzing these spectral lines in detail. in
ANALYSIS
The following Hamiltonian was employed for both the upper and lower vibrational states to analyze the observed spectral lines: H = AN; + BNi + CN; - Ati4 - A,fi*N: - SdN:(Nz, - N:) + (N’b- N:)N:]
+
- AKN;f - 2Sfl*(Na
- Nf)
$,N6 + *,Nf14N2,
kdl4 ZEEMAN
I
FIG. 3. A part of the observed CHzF ~3spectrum. The upper trace is obtained with Zeeman modulation, whereas the lower trace is recorded by discharge current modulation.
104
YAMADA AND HIROTA TABLE I Observed Transitions of the vj Band of CHIF (cm-‘) Transition
Obs-Calc
Obs
Weight
K," KC"
N' K,' Kc'
N”
2 2 3 3 4 5 5
2 2 2 2 2 2 2
1 0 2 1 3 4 3
2 2 3 3 4 5 5
2 2 2 2 2 2 2
0 1
3 3 4 4
3 3 3 3
0 1 2 1
3 3 4 4
4 4 5 5 6 6 7 7 8 8 9 9 12 12
4 4 4 4 4 4 4 4 4 4 4 4 4 4
0 1 2 1 3 2 4 3 5 4 6 5 8 9
5 5 6 6 7 7
5 5 5 5 5 5
6 6 7 7 8 8 10 10 11 11 12 12
1 2 2 3 4
1170.305 1170.305 1170.238 1170.247 1170.145 1170.023 1170.087
78 78 04 36 34 14 26
0.001 -0.000 -0.000 -0.000 -0.000 -0.001 -0.000
49 33 38 22 96 15 97
0.707 0.707 1.000 1.000 1.000 1.000 1.000
3 3 3 3
1 0 1 2
1170.178 1170.178 1170.099 1170.099
63 63 98 98
-0.001 -0.001 0.000 0.000
48 47 33 27
0.707 0.707 0.707 o.io7
: 5 5 6 6 7 7 8 8 9 9 12 12
4 4 4 4 4 4 4 4 4 4 4 4 4 4
1 0 1 2 2 3 3 4 4 5 5 6 9 8
1170.005 1170.005 1169.908 1169.908 1169.792 1169.792 1169.657 1169.657 1169.504 1169.504 1169.330 1169.330 1168.716 1168.716
13 13 44 44 87 87 97 97 28 28 67 67 18 18
-0.001 -0.001 -0.000 -0.000 0.000 0.000 0.001 0.001 0.001 0.001 -0.000 -0.000 -0.001 -0.000
20 20 47 46 55 56 12 12 38 37 34 39 12 60
0.707 0.707 0.707 0.707 0.707 0.707 0.707 0.707 0.707 0.707 0.707 0.707 0.707 0.707
1 0 2 1 3 2
5 5 6 6 7 7
5 5 5 5 5 5
0 1 1 2 2 3
1169.784 1169.784 1169.670 1169.670 1169.536 1169.536
70 70 30 30 58 58
0.000 0.000 0.000 0.000 0.000 0.000
67 67 57 58 11 10
0.707 0.707 0.707 0.707 0.707 0.707
6 6 6 6 6 6 6 6 6 6 6 6
1 0 2 1 3 2 5 4 6 5 7 6
6 6 7 7 8 8 10 10 11 11 12 12
6 6 6 6 6 6 6 6 6 6 6 6
0 1 1 2 2 3 4 5 5 6 6 7
1169.519 1169.519 1169.384 1169.384 1169.231 1169.231 1168.867 1168.867 1168.657 1168.657 1168.427 1168.427
03 03 15 15 08 08 04 04 64 64 65 65
0.000 0.000 -0.000 -0.000 -0.000 -0.000 -0.000 -0.000 0.000 0.000 0.000 0.000
92 92 63 64 81 81 60 60 85 84 12 10
0.707 0.707 0.707 0.707 0.707 0.707 0,707 0.707 0.707 0.707 0.707 0.707
10 10
7 7
3 4
10 10
7 7
4 3
1168.682 1168.682
81 81
0.000 0.000
20 18
0.707 0.707
4 4 4 4 4 4 4
1 2 2 3 3 4 4
3 2 3 1 2 0 1
1 2 2 3 3 4 4
4 3 4 2 3 1 2
1160.074 1160.354 1160.381 1160.314 1160.314 1160.224 1160.224
91 83 93 44 44 76 76
0.000 0.000 0.000 0.000 -0.000 -0.000 -0.000
69 27 15 03 14 42 42
1.000 1.000 1.000 0.707 0.707 0.707 0.707
5 5 5 5 5
: 3 3 4
: 2 3 2
2 2 3 3 4
4 5 3 4 3
1158.277 1158.328 1158.257 1158.257 1158.172
67 15 51 51 07
0.000 0.000 0.001 0.000 0.000
30 05 40 89 70
1.000 1.000 0.707 0.707 0.707
DIODE LASER SPECTROSCOPY OF CHzF
105
~3
TABLE I-Continued Obs
Transition N’
K,' Kc'
N”
Obs-Calc
Weight
K," KC"
5 5 5
4 5 5
1 0 1
6 6 6
4 5 5
2 1 2
1158.172 1158.050 1158.050
07 94 94
0.000
69
-0.000 -0.000
70 69
0.707 0.707 0.707
6 6 6 6
3 3 4 4
3 4 2 3
7 7 7 7
3 3 4 4
4 5 3 4
1156.178 1156.178 1156.099 1156;099
30 30 05 05
0.000 -0.000 0.000 0.000
76 46 73 72
0.707 0.707 0.707 0.707
9 9 9 9 9 9
18 2 4 4 6 6
7 5 6 3 4
10 10 10 10 10 10
19 2 4 4 6 6
8 6 7 4 5
1149.118 1149.668 1149.765 1149.765 1149.517 1149.517
36 39 90 90 46 46
0.000 0.000 -0.001 -0.001 -0.000 -0.000
18 48 15 24 40 40
1.000 1.000 0.707 0.707 0.707 0.707
11 11 11 11 11 11 13 3 6 6
2 2 3 3 6 6 2 13
9 10 8 9 5 6 12
12 12 12 12 12 12 14 2
2 2 3 3 6 6 2
10 11 9 10 6 7 13
t
: 4
2 1 2
6 7 8
7
5 9
2 2 2
z 2
2 7
1145.162 1145.720 1145.490 1145.512 1145.209 1145.209 1141.468 1176.034 1181.529 1181.529 1185.310 1185.294 1187.081
84 68 03 05 27 27 28 75 89 89 03 12 82
-0.000 48 0.000 14 0.002 84 -0.001 35 -0.000 14 -0.000 16 0.000 00 0.001 54 0.000 04 0.000 05 -0.000 70 -0.002 03 0.000 82
x
1.000 1.000
1.000 1.000 0.707 0.707 1.000 1.000 0.707 0.707 1.000 1.000 1.000
The spin-rotation splittings were first eliminated by appropriately averaging spin doublet wavenumbers, to obtain hypothetical unsplit wavenumbers, which are listed in Table I. Unresolved K doublets were given the weight l/E. The observed spin-rotation splittings were analyzed separately by using an approximate expression given by 6u = Y(N + l/2),
(2)
where
+ 1)l + (ebb+ 4/2. Y = [GZ,- (Q, + d4J3WW (3) By fixing ground state parameters to the microwave values of Ref. (.3), we have determined upper state constants and the band origin by the least-squares method. Table II lists the derived constants as well as those assumed for the ground state for comparison. The quality of the fit may be judged from the observed-calculated wavenumbers shown in Table I; the standard deviation of the fit is 0.000 76 cm-‘, which is of the same magnitude as the experimental error. The observed spin-rotation splittings are listed in Table III together with the coupling constants derived therefrom. DISCUSSION
The band origin 1170.4165(6) cm-’ obtained by the present study favorably compares with the matrix value 1163 cm-‘; the discrepancy of 0.63% is of reasonable magnitude as the matrix shift (10).
106
YAMADA AND HIROTA TABLE II Molecular Constants of CHIF (cm-‘)
constant A
B C
Ground
8.846 1.032 0.924 0.260 0.378 0.647 0.28 0.342
v 3 =1 b
statea
119 8 324 9 898 95
1 91 2
8.823 1.016 0.919
745(81) 588(64) 490(84)
0.175(41) -0.442(15) 0.801 2(39) 0.270(43) 1.136 (28) 0.83(15) 0.77 (15) -0.163 8(59) 0.275 1183) 1170.416
vO
45(56)
a. Fixed to the microwave value, Ref. (3), b. Values in parentheses denote one stazdard deviation apply to the last digits of the constants.
and
Inspection of Table II reveals (1) that the inertial defect is negative (-0.159 amu A’) in the 21~= 1 state, (2) that the centrifugal distortion constant ANKchanges sign upon u3 excitation, and (3) that a few N6 terms are required for the 213= 1 state. A TABLE III Observed Spin-Rotation Splittings and Interaction Constants (cm-‘) Transition
Obs-Calc
Obs
43 - 53
-0.005
53
0.001
91
44 - 54
-0.011
13
0.000
57
54 - 64
-0.009
93
-0.001
77
55 - 65a
-0.018
79
0.007
85
0.012
69
-0.000
21
'6 - lo6
-0.006
69
0.000
04
Constant
Ground
stateb
Eaa
-0.035
890 23
-0.033
'bb
-0.006
196 6
-0.008
50(83)
SC
-0.000
047 13
-0.000
047 13d
64 - 54
a. b. c. d.
v3=1C
61(48)
Not included in the fit. Microwave results (21 and fixed. Values in parentheses denote one standard deviation and apply to the last digits of the constants. Fixed to the ground state value.
DIODE LASER SPECTROSCOPY OF CH2F v3
107
similar observation has been reported on the 19band of H&O (II), for which ANKis negative when v3is treated as an isolated band, but the inertial defect is positive and apparently no higher order centrifugal distortion terms are necessary in fitting the observed spectrum. When the Coriolis interactions with u4 and Vgwere taken into account, ANKof H2C0 became positive. While the V6band has not been identified for H2CF, it has been estimated to be at 953 cm-’ for H$Br in matrices (12). It is therefore conceivable that the CH2 rocking state (4) comes close to the u3 = 1 state. The CH2 wagging or v4 mode, on the other hand, is quite low in frequency in CHPF (3), but, because this mode may be of double-minimum type, the 3v4 state may also be located quite close to the v3 state. ACKNOWLEDGMENT Numericalcalculationsin the present study were carried out at the Computer Center of the Institute for MolecularScience. RECEIVED:
September 19, 1985 REFERENCES
1. C. YAMADA, E. HIROTA,AND K. KAWAGUCHI,J. Chem. Phys. 75,5256-5264 (198 I). 2. C. YAMADAANDE. HIROTA,J. Chem. Phys. 78, 1703-1711 (1983). 3. Y. ENDO,C. YAMADA,S. SAITO,ANDE. HIROTA,.I. Chem. Phys. 79, 1605-161 I (1983). 4. M. E. JAC~XANDD. E. MILLIGAN,J. Chem. Phys. 50,3252-3262 (1969).
5. J. I. RAYMONDANDL. ANDREWS,J. Phys. Chem. 75,3235-3242 (1971). 6. M. E. JACOX,Chem. Phys. 59, 199-212 (198 1). 7. C. YAMADA, K. NAGAI,ANDE. HIROTA,J. Mol. Spectrosc.85,416-426 (198 1). 8. Y. ENDO,K. NAGAI,C. YAMADA,AND E. HIROTA,J. Mol. Speclrosc.97,213-219 (1983). 9. W. B. ORSON,A. G. MAKI, ANDW. J. LAFFERTY, J. Phys. Chem. Ref: Data 10,1065-1084 (1981). 10. M. E. JACOX,J. Phys. Chem. Ref: Data 13,945-1068 (1984). 11. M. ALLEGRINI, J. W. C. JOHNS,ANDA. R. W. MCKELLAR,J. Mol. Specfrosc. 66,69-78 (1977). 12. D. W. SMITHANDL. ANDREWS,J. Chem. Phys. 55,5295-5303 (197 1).
OF MOLECULAR
SPECTROSCOPY
116, 101-107 (1986)
Infrared Diode Laser Spectroscopy of the v3 Band of the Fluoromethyl Radical, CH2F CHIKASHIYAMADA AND EIZI HIROTA Institutefor MolecularScience, Okazaki444, Japan The v, (C-F stretching) band of the CHrF radical was observed with Doppler-limited resolution, by using infrared diode laser spectroscopy with Zeeman and discharge current modulatjon. The CH,F radical was generated directly in a multiple retkction absorption cefl by the electrical discharge in CH2FCOOCHs. The observed spectrum was analyzed to yield the band origin of 1170.4165(6) cm-’ with one standard error in parentheses, in addition to the rotational constants, centrifugal distortion constants, and spin-rotation interaction constants in the uL)) = 1 state. 0 1986 Academic pnss. Inc.
INTRODUCTION
The planarity of the methyl radical (1) does not subsist anymore when we replace the three hydrogen atoms with fluorine atoms, namely, the CF3 radical has a quite rigid pyramidal structure (2). We then expect that either CHzF or CHF2 or both may exhibit the effect of the inversion in their high-resolution spectra. In a previous paper (3), we have reported the microwave spectrum of CHzF and have shown that the molecule is almost, but not completely, planar. This microwave study was motivated by an infrared diode laser observation of the u3 band, which is described in the present paper. No vibrational spectrum has been reported for CH2F in the gas phase. Jacox and Mill&n (4), Raymond and Andrews (5), and Jacox (6) have identified only the C-F stretching band at 1163 cm-’ in low-temperature matrices. Endo et al. (3) have observed a set of vibrational satellites, which they assigned to the out-of-plane bending or CH2 wagging u4 = 1 state, based upon relative intensity measurements leading to an estimated excitation energy of about 300 cm-’ and upon the observed nuclear spin statistical weight. EXPERIMENTAL
DETAILS
The infrared diode laser spectrometer employed is a Zeeman-modulated spectrometer equipped with a White-type multiple-reflection absorption cell (7). Discharge current modulation described in a previous paper (8) was also used to detect lines with small Zeeman effects. The magnetic field for Zeeman modulation consists of an AC field of 860 Hz with 700 G peak-to-peak superimposed on a DC field of 350 G. Discharge current modulation was combined with conventional source-frequency modulation; the source diode was frequency modulated by a IO-kHz sine wave and the absorption signal, after demodulation by a lock-in amplifier tuned to 10 kHz, was 101
0022-2852186 $3.00 Copyright 0 1986 by Academic Press, Inc. All rights of reproduction in any form rescwcd.
102
YAMADA AND HIROTA
fed to a second lock-in amplifier operated at 150 to 200 Hz, the frequency at which the discharge current was switched on and off. The CHzF radical was found to be most effectively produced by the electrical discharge in methyl fluoroacetate CHPFCOOCHs of 100 mTorr diluted with either Ar or N2 of 400 mTorr. We also tested methyl fluoride as a precursor, as in the microwave study (3), namely, the electrical discharge in a mixture of CHsF and CF, or of CH3F and SF, and the reaction of CHsF with microwave discharge products of CF,, but none of these systems gave spectra of CHlF stronger than those derived from CH2FCOOCH3. In addition, the precursor CHsF exhibited a number of strong lines which interfered with the observation of the CHzF signal. The wavenumbers of CHlF lines were measured using NzO spectral lines (9) as references and a vacuum-spaced confocal etalon (free spectral range of about 0.01 cm-‘) as an interpolation device. OBSERVED SPECTRUM
The wavenumber region from 1139 to 1188 cm-’ was scanned, of which 65% was covered because of mode gaps. Figure 1 shows a part of the observed spectrum around 1170 cm-’ recorded with Zeeman modulation; four Q-branch series are seen. It clearly indicates that odd K, branches are weaker than even K, branches. This observation is consistent with the fact that the vibronic symmetry in the ground state is Bi . No spin-rotation splittings were resolved for Q-branch transitions. Figure 2 shows the K structure of the P(6) transition, The splitting for the K, = 2 line is due to the asymmetry of the molecule, whereas the splittings for the I(, = 3,4, and 5 lines are caused by the spin-rotation interaction. The K, = 0 transition does not appear in Fig. 2, because its Zeeman effect is too small to be used for modulation, and the K, = 1 transitions are located outside the region covered by the diode. Figure 3 compares the P(5) transitions observed by Zeeman modulation and discharge current modulation. It is to be noted that the K, = 1 line appears only in the discharge-currentmodulated spectrum.
qQ3 qQ
7 ?
6
qQ5 ‘O6
7 7
7
4 5
3
4
5
6
I
1169.5 FIG.
6
6 6
1
1170.0
1. Q-branch transitions of the CHzF v3band recorded with Zeeman modulation.
103
DIODE LASER SPECTROSCOPY OF CH2F v3 P(6) Ka
N20 1158.19614cm-’ !
RG. 2. The P(6) transition of the CHIF v3band observed by Zeeman modulation. The middle trace shows an N20 reference line, and the bottom trace represents the fringe pattern generated by a confocal etalon of a free spectral range of about 0.01 cm-‘.
We have assigned 25 Q-branch, 22 P-branch, and 5 R-branch transitions, as listed Table I. All the assigned lines obey u-type selection rules. Several lines are left unassigned, as exemplified by a few lines in Fig. 3. These unassigned lines are probably due to hot band transitions from the o4 = 1 state, but, because the observed data are rather limited, it does not seem to warrant analyzing these spectral lines in detail. in
ANALYSIS
The following Hamiltonian was employed for both the upper and lower vibrational states to analyze the observed spectral lines: H = AN; + BNi + CN; - Ati4 - A,fi*N: - SdN:(Nz, - N:) + (N’b- N:)N:]
+
- AKN;f - 2Sfl*(Na
- Nf)
$,N6 + *,Nf14N2,
kdl4 ZEEMAN
I
FIG. 3. A part of the observed CHzF ~3spectrum. The upper trace is obtained with Zeeman modulation, whereas the lower trace is recorded by discharge current modulation.
104
YAMADA AND HIROTA TABLE I Observed Transitions of the vj Band of CHIF (cm-‘) Transition
Obs-Calc
Obs
Weight
K," KC"
N' K,' Kc'
N”
2 2 3 3 4 5 5
2 2 2 2 2 2 2
1 0 2 1 3 4 3
2 2 3 3 4 5 5
2 2 2 2 2 2 2
0 1
3 3 4 4
3 3 3 3
0 1 2 1
3 3 4 4
4 4 5 5 6 6 7 7 8 8 9 9 12 12
4 4 4 4 4 4 4 4 4 4 4 4 4 4
0 1 2 1 3 2 4 3 5 4 6 5 8 9
5 5 6 6 7 7
5 5 5 5 5 5
6 6 7 7 8 8 10 10 11 11 12 12
1 2 2 3 4
1170.305 1170.305 1170.238 1170.247 1170.145 1170.023 1170.087
78 78 04 36 34 14 26
0.001 -0.000 -0.000 -0.000 -0.000 -0.001 -0.000
49 33 38 22 96 15 97
0.707 0.707 1.000 1.000 1.000 1.000 1.000
3 3 3 3
1 0 1 2
1170.178 1170.178 1170.099 1170.099
63 63 98 98
-0.001 -0.001 0.000 0.000
48 47 33 27
0.707 0.707 0.707 o.io7
: 5 5 6 6 7 7 8 8 9 9 12 12
4 4 4 4 4 4 4 4 4 4 4 4 4 4
1 0 1 2 2 3 3 4 4 5 5 6 9 8
1170.005 1170.005 1169.908 1169.908 1169.792 1169.792 1169.657 1169.657 1169.504 1169.504 1169.330 1169.330 1168.716 1168.716
13 13 44 44 87 87 97 97 28 28 67 67 18 18
-0.001 -0.001 -0.000 -0.000 0.000 0.000 0.001 0.001 0.001 0.001 -0.000 -0.000 -0.001 -0.000
20 20 47 46 55 56 12 12 38 37 34 39 12 60
0.707 0.707 0.707 0.707 0.707 0.707 0.707 0.707 0.707 0.707 0.707 0.707 0.707 0.707
1 0 2 1 3 2
5 5 6 6 7 7
5 5 5 5 5 5
0 1 1 2 2 3
1169.784 1169.784 1169.670 1169.670 1169.536 1169.536
70 70 30 30 58 58
0.000 0.000 0.000 0.000 0.000 0.000
67 67 57 58 11 10
0.707 0.707 0.707 0.707 0.707 0.707
6 6 6 6 6 6 6 6 6 6 6 6
1 0 2 1 3 2 5 4 6 5 7 6
6 6 7 7 8 8 10 10 11 11 12 12
6 6 6 6 6 6 6 6 6 6 6 6
0 1 1 2 2 3 4 5 5 6 6 7
1169.519 1169.519 1169.384 1169.384 1169.231 1169.231 1168.867 1168.867 1168.657 1168.657 1168.427 1168.427
03 03 15 15 08 08 04 04 64 64 65 65
0.000 0.000 -0.000 -0.000 -0.000 -0.000 -0.000 -0.000 0.000 0.000 0.000 0.000
92 92 63 64 81 81 60 60 85 84 12 10
0.707 0.707 0.707 0.707 0.707 0.707 0,707 0.707 0.707 0.707 0.707 0.707
10 10
7 7
3 4
10 10
7 7
4 3
1168.682 1168.682
81 81
0.000 0.000
20 18
0.707 0.707
4 4 4 4 4 4 4
1 2 2 3 3 4 4
3 2 3 1 2 0 1
1 2 2 3 3 4 4
4 3 4 2 3 1 2
1160.074 1160.354 1160.381 1160.314 1160.314 1160.224 1160.224
91 83 93 44 44 76 76
0.000 0.000 0.000 0.000 -0.000 -0.000 -0.000
69 27 15 03 14 42 42
1.000 1.000 1.000 0.707 0.707 0.707 0.707
5 5 5 5 5
: 3 3 4
: 2 3 2
2 2 3 3 4
4 5 3 4 3
1158.277 1158.328 1158.257 1158.257 1158.172
67 15 51 51 07
0.000 0.000 0.001 0.000 0.000
30 05 40 89 70
1.000 1.000 0.707 0.707 0.707
DIODE LASER SPECTROSCOPY OF CHzF
105
~3
TABLE I-Continued Obs
Transition N’
K,' Kc'
N”
Obs-Calc
Weight
K," KC"
5 5 5
4 5 5
1 0 1
6 6 6
4 5 5
2 1 2
1158.172 1158.050 1158.050
07 94 94
0.000
69
-0.000 -0.000
70 69
0.707 0.707 0.707
6 6 6 6
3 3 4 4
3 4 2 3
7 7 7 7
3 3 4 4
4 5 3 4
1156.178 1156.178 1156.099 1156;099
30 30 05 05
0.000 -0.000 0.000 0.000
76 46 73 72
0.707 0.707 0.707 0.707
9 9 9 9 9 9
18 2 4 4 6 6
7 5 6 3 4
10 10 10 10 10 10
19 2 4 4 6 6
8 6 7 4 5
1149.118 1149.668 1149.765 1149.765 1149.517 1149.517
36 39 90 90 46 46
0.000 0.000 -0.001 -0.001 -0.000 -0.000
18 48 15 24 40 40
1.000 1.000 0.707 0.707 0.707 0.707
11 11 11 11 11 11 13 3 6 6
2 2 3 3 6 6 2 13
9 10 8 9 5 6 12
12 12 12 12 12 12 14 2
2 2 3 3 6 6 2
10 11 9 10 6 7 13
t
: 4
2 1 2
6 7 8
7
5 9
2 2 2
z 2
2 7
1145.162 1145.720 1145.490 1145.512 1145.209 1145.209 1141.468 1176.034 1181.529 1181.529 1185.310 1185.294 1187.081
84 68 03 05 27 27 28 75 89 89 03 12 82
-0.000 48 0.000 14 0.002 84 -0.001 35 -0.000 14 -0.000 16 0.000 00 0.001 54 0.000 04 0.000 05 -0.000 70 -0.002 03 0.000 82
x
1.000 1.000
1.000 1.000 0.707 0.707 1.000 1.000 0.707 0.707 1.000 1.000 1.000
The spin-rotation splittings were first eliminated by appropriately averaging spin doublet wavenumbers, to obtain hypothetical unsplit wavenumbers, which are listed in Table I. Unresolved K doublets were given the weight l/E. The observed spin-rotation splittings were analyzed separately by using an approximate expression given by 6u = Y(N + l/2),
(2)
where
+ 1)l + (ebb+ 4/2. Y = [GZ,- (Q, + d4J3WW (3) By fixing ground state parameters to the microwave values of Ref. (.3), we have determined upper state constants and the band origin by the least-squares method. Table II lists the derived constants as well as those assumed for the ground state for comparison. The quality of the fit may be judged from the observed-calculated wavenumbers shown in Table I; the standard deviation of the fit is 0.000 76 cm-‘, which is of the same magnitude as the experimental error. The observed spin-rotation splittings are listed in Table III together with the coupling constants derived therefrom. DISCUSSION
The band origin 1170.4165(6) cm-’ obtained by the present study favorably compares with the matrix value 1163 cm-‘; the discrepancy of 0.63% is of reasonable magnitude as the matrix shift (10).
106
YAMADA AND HIROTA TABLE II Molecular Constants of CHIF (cm-‘)
constant A
B C
Ground
8.846 1.032 0.924 0.260 0.378 0.647 0.28 0.342
v 3 =1 b
statea
119 8 324 9 898 95
1 91 2
8.823 1.016 0.919
745(81) 588(64) 490(84)
0.175(41) -0.442(15) 0.801 2(39) 0.270(43) 1.136 (28) 0.83(15) 0.77 (15) -0.163 8(59) 0.275 1183) 1170.416
vO
45(56)
a. Fixed to the microwave value, Ref. (3), b. Values in parentheses denote one stazdard deviation apply to the last digits of the constants.
and
Inspection of Table II reveals (1) that the inertial defect is negative (-0.159 amu A’) in the 21~= 1 state, (2) that the centrifugal distortion constant ANKchanges sign upon u3 excitation, and (3) that a few N6 terms are required for the 213= 1 state. A TABLE III Observed Spin-Rotation Splittings and Interaction Constants (cm-‘) Transition
Obs-Calc
Obs
43 - 53
-0.005
53
0.001
91
44 - 54
-0.011
13
0.000
57
54 - 64
-0.009
93
-0.001
77
55 - 65a
-0.018
79
0.007
85
0.012
69
-0.000
21
'6 - lo6
-0.006
69
0.000
04
Constant
Ground
stateb
Eaa
-0.035
890 23
-0.033
'bb
-0.006
196 6
-0.008
50(83)
SC
-0.000
047 13
-0.000
047 13d
64 - 54
a. b. c. d.
v3=1C
61(48)
Not included in the fit. Microwave results (21 and fixed. Values in parentheses denote one standard deviation and apply to the last digits of the constants. Fixed to the ground state value.
DIODE LASER SPECTROSCOPY OF CH2F v3
107
similar observation has been reported on the 19band of H&O (II), for which ANKis negative when v3is treated as an isolated band, but the inertial defect is positive and apparently no higher order centrifugal distortion terms are necessary in fitting the observed spectrum. When the Coriolis interactions with u4 and Vgwere taken into account, ANKof H2C0 became positive. While the V6band has not been identified for H2CF, it has been estimated to be at 953 cm-’ for H$Br in matrices (12). It is therefore conceivable that the CH2 rocking state (4) comes close to the u3 = 1 state. The CH2 wagging or v4 mode, on the other hand, is quite low in frequency in CHPF (3), but, because this mode may be of double-minimum type, the 3v4 state may also be located quite close to the v3 state. ACKNOWLEDGMENT Numericalcalculationsin the present study were carried out at the Computer Center of the Institute for MolecularScience. RECEIVED:
September 19, 1985 REFERENCES
1. C. YAMADA, E. HIROTA,AND K. KAWAGUCHI,J. Chem. Phys. 75,5256-5264 (198 I). 2. C. YAMADAANDE. HIROTA,J. Chem. Phys. 78, 1703-1711 (1983). 3. Y. ENDO,C. YAMADA,S. SAITO,ANDE. HIROTA,.I. Chem. Phys. 79, 1605-161 I (1983). 4. M. E. JAC~XANDD. E. MILLIGAN,J. Chem. Phys. 50,3252-3262 (1969).
5. J. I. RAYMONDANDL. ANDREWS,J. Phys. Chem. 75,3235-3242 (1971). 6. M. E. JACOX,Chem. Phys. 59, 199-212 (198 1). 7. C. YAMADA, K. NAGAI,ANDE. HIROTA,J. Mol. Spectrosc.85,416-426 (198 1). 8. Y. ENDO,K. NAGAI,C. YAMADA,AND E. HIROTA,J. Mol. Speclrosc.97,213-219 (1983). 9. W. B. ORSON,A. G. MAKI, ANDW. J. LAFFERTY, J. Phys. Chem. Ref: Data 10,1065-1084 (1981). 10. M. E. JACOX,J. Phys. Chem. Ref: Data 13,945-1068 (1984). 11. M. ALLEGRINI, J. W. C. JOHNS,ANDA. R. W. MCKELLAR,J. Mol. Specfrosc. 66,69-78 (1977). 12. D. W. SMITHANDL. ANDREWS,J. Chem. Phys. 55,5295-5303 (197 1).