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K = 3 splitting and quadrupole hyperfine structure in the ν1 fundamental of nitrogen trifluoride
JOURNAL
OF MOLECULAR
SPECTROSCOPY
(1991)
150,28-32
K = 3 Splitting and Quadrupole Hyperfine Structure in the v1 Fundamental of Nitrogen Trifluoride W. HOHE AND W. A. KREINER Abteilung Physikalische Chemie, Universittit Urn, D-7900 Urn, West Germany We have investigated the vi fundamental band of “‘NF3 at 1032 cm-’ using the infrared laser sideband technique, resolving the quadrupole hyperfme structure as well as splittings on some high-J K = 3 transitions. 0 1991 Academic Press, Inc.
NF3 is widely used industrially in plasma etching processes and for fluorination of organic materials. Nevertheless, the most recent infrared and Raman investigations for this molecule date from 1967 (1-4). Microwave investigations have been performed since the early days of rotational spectroscopy (5-7). Sheridan and Gordy have determined the ground state structure and the nuclear quadrupole moment (5), and Otake et al. have studied various excited states (8)) while Ghosh et al. have measured its electric dipole moment (9). A recording of the millimeter-wave spectrum by Mirri and Cazzoli was dedicated to the determination of the B constant and centrifugal distortion constants (10). We have applied the saturation technique employing CO2 laser modulation sidebands as a tunable infrared source to investigate sub Doppler splitting effects. The spectrometer has been described already ( 1I ) . It provides a res-
J23
A_
1
K3
‘+
,A+
v, R 2293
-
A_
A2 At J22
A+
K3
FIG. 1. Observed K = 3 infrared transition in the R branch of the Y, fundamental of NF, exhibiting vibration-rotational splitting. Vibration-rotational interaction lifts the AlA* degeneracy of K = 3 levels. Inversion splitting is regarded to be negligible. Due to spin statistics only one component of the inversion doublet has nonzero intensity. 0022-2852191 $3.00 Copy-@bt
0 1991 by Academic
All rights of reproduction
28 Press, Inc.
in any form resewed.
NITROGEN
19
TRIFLUORIDE
olution of approximately 300 kHz. For an absorption cell we used a l-m glass tube; the sample was used without further purification. The signals were recorded with frequency modulation at 60 kHz and 2fphase sensitive detection. In symmetric top molecules higher order vibration-rotational interaction may split the otherwise degenerate A I and A1 components of (K, 1) levels, 1being the quantum number indicating the vibrational angular momentum along the symmetry axis ( 12,
9
Nki
i
R 22,3
-I
1MHz
I-
i
FIG. 2. Series of R-branch transitions with J = 16, 22. 23. 31, and 33 with A’ = 3 splitting in the V, fundamental of NF, (R( 16.3) not resolved). Resolution of these 5 MHz scans is about 300 kHz. Frequency modulation and phase sensitive 2f detection at 60 kHz were applied. The large spike in the bottom trace is an artifact produced by the MW signal source, but greatly enhanced because more than 100 scans had been added up for this recording.
30
HijHE AND KREINER
13). In our case splitting occurs for levels with K = 3n, the effect on the K = 3 levels being dominant. The situation is similar to that for phosphine (14-16). The symmetry species A, and AZ of C,, are related to the A+ and A_ species in a way described in Ref. (16). Neglecting centrifugal distortion corrections and the resonance term which affects only the A+ component of K = 3, the splitting is given by the expression Au = {(J + K)!/(J
- K)! >a q(K, I).
(1)
As an example, Fig. 1 shows K = 3 levels of NF, in the ground and in the v1 (A,) excited state together with observed infrared transitions. We have assumed a level scheme with the A_ above the A+ levels. Figure 2 gives the K = 3 transitions on which splitting could be resolved so far. The sideband frequencies listed in Table I refer to the centers of the doublets with an error in frequency measurement of 1O-5 cm-’ or less. For each transition several recordings have been averaged. The q values derived from a fit seem to indicate a situation where the upper levels in the ground and in the excited state are connected. Assuming a crossover situation, i.e., the upper ground state level connected to the lower excited state level, leads to one of the q constants being negative. The separation of the A+A_ doublets (in kHz) and the q constants (in Hz) are given with uncertainties indicated being one standard error. Among the more than 100 saturation dips observed so far in the infrared spectrum of the v1 fundamental there were 10 transitions showing quadrupole structure, among them the P( 3, 2) transition where only the excited state is split. Examples are given in Fig. 3. The transitions P(3, 0) and P( 3, 2) had been recorded with the upper sideband of the P( 38) line in the 9 pm band of the COZ laser, the transition P( 19, 15) with the lower sideband of 9 P( 20). Using the expression for the quadrupole interaction energy
esQ{(3K2/J(J+ 1) - W-U,
J,
(2)
F),
with f( I, J, F) being Casimir’s function, we obtained the values given in Table II,
TABLE I Vibration-Rotational Transition
Laser CO2
9w
Splitting in the u, R Branch of NF,
Sideband/MHz (center
Splitting
of doublet)
obs./kHz
IXlC./kHZ
J, K R 16.3
P 22
R 22, 3
P
18
+ 14 046.980
375 (14)
374.9 (51)
R
P 16
-16 084.503
458 (26)
458.2 (57)
23.3
-14 891.592
not resolved
R
31, 3
P 10
+ 16 686.296
1740 (18)
1738.8 (70)
R
33, 3
P
+ 14 070.656
2288 (25)
2288.2 (95)
8
q (3,O) excited state
0.01229
(39) Hz
q (3,0) ground state
0.01304
(47) Hz
NITROGEN
-I
1MHr
31
TRIFLUORIDE
I-
ll
I
FIG. 3. Quadrupole splitting on the transitions P(3, O), P( 3, 2). and R( 19, 15). The range of the scans is 5 MHz. Among the more than 100 transitions in the Y, fundamental of NF, observed with saturation spectroscopy there were 10 with resolvable quadrupole hyperfine structure. In the case of the P( 3. 2) there is no splitting of the ground state level and all three components could be separated.
which are compared with the results obtained from microwave observations ( 9). Our values agree with the microwave data within the standard error which is one times r.m.s. in our case, but do not differ significantly between the ground and the excited state.
TABLE II eQq Values for NF3 in the Ground and Y, Excited State Microwave
This work MHZ ground state VI state
(Ref. 5)
7.088
(30)
- 7.07 (10)
- 7.082
(32)
____.
(Ref. 8) 7.01
(6)
6.92 (20)
32
HOHE AND KREINER ACKNOWLEDGMENT
Financial support of the Deutsche Forschungsgemeinschaft and of the Fonds der Chemischen Industrie isgratefully acknowledged. We also thank the Solvay Fhtor und Derivate GmbH/Soltronic GmbH, Hannover, for providing us with a sample of nitrogen trifluoride. RECEIVED:
June 10, 1991 REFERENCES
1. R. J. L. POPPLEWELL, F. N. MASRI,AND H. W. THOMPSON,Spectrochim. Acta Part A 23,2197-2807 (1967). 2. J. SHAMIRAND H. H. HYMAN, Spectrochim. Acta Part A 23, 1899-1901 (1967). 3. A. ALLAN,J. L. DUNCAN,J. H. HOLLOWAY,ANDD. MCKEAN, J. Mol. Spectrosc. 31,368-377 ( 1968). 4. A. C. JEANNOTTE II AND JOHNOVEREND,Spectrochim. Acta Part A 33, 1067-107 1 ( 1977). 5. J. SHERIDANAND W. GORDY, Phys. Rev. 79, 513-515 ( 1950). 6. C. M. JOHNSON,R. TRAMBARULO, AND W. GORDY, Phys. Rev. 84, 1178-l 180 ( 1951). 7. M. COWANAND W. G~RDY, Bull. Am. Phys. SOC.Ser. II 5,241 ( 1960). 8. M. OTAKE, C. MATSUMURA,AND Y. MORINO,J. Mol. Spectrosc. 28, 316-324 (1968); 28, 325-340 (1968). 9. S. N. GHOSH,R. TRAMBARULO, AND W. GORDY, J. Chem. Phys. 21,308-310 ( 1953). IO. A. M. MIRRIAND G. CAZZOLI,J. Chem. Phys. 47, 1197-l 198 ( 1967). Il. H. PRINZ,W. HOHE, W. A. KREINER,M. LOETE,J. HILICO,G. PIERRE,AND G. MAGERL,J. Mol. Spectrosc. 135, 144-160 ( 1989). 12. T. OKA, J. Chem. Phys. 47,5410-5426 (1967). 13. D. PA~~IJSEK AND M. R. ALIEV,“Molecular Vibrational/Rotational Spectra,” Academia, Prague, 1982. 14. P. B. DAVIES,R. M. NEUMANN,S. C. WOFSY, AND W. KLEMPERER, J. Chem. Phys. 55, 3564-3568 (1971). IS. S. TANIMURAAND K. TAKAGI, J. Mol. Spectrosc. 104,4 14-4 16 ( 1984). 16. G. TARRAGOAND M. DANG NHU, J. Mol. Spectrosc. 111,425-439 ( 1985).
OF MOLECULAR
SPECTROSCOPY
(1991)
150,28-32
K = 3 Splitting and Quadrupole Hyperfine Structure in the v1 Fundamental of Nitrogen Trifluoride W. HOHE AND W. A. KREINER Abteilung Physikalische Chemie, Universittit Urn, D-7900 Urn, West Germany We have investigated the vi fundamental band of “‘NF3 at 1032 cm-’ using the infrared laser sideband technique, resolving the quadrupole hyperfme structure as well as splittings on some high-J K = 3 transitions. 0 1991 Academic Press, Inc.
NF3 is widely used industrially in plasma etching processes and for fluorination of organic materials. Nevertheless, the most recent infrared and Raman investigations for this molecule date from 1967 (1-4). Microwave investigations have been performed since the early days of rotational spectroscopy (5-7). Sheridan and Gordy have determined the ground state structure and the nuclear quadrupole moment (5), and Otake et al. have studied various excited states (8)) while Ghosh et al. have measured its electric dipole moment (9). A recording of the millimeter-wave spectrum by Mirri and Cazzoli was dedicated to the determination of the B constant and centrifugal distortion constants (10). We have applied the saturation technique employing CO2 laser modulation sidebands as a tunable infrared source to investigate sub Doppler splitting effects. The spectrometer has been described already ( 1I ) . It provides a res-
J23
A_
1
K3
‘+
,A+
v, R 2293
-
A_
A2 At J22
A+
K3
FIG. 1. Observed K = 3 infrared transition in the R branch of the Y, fundamental of NF, exhibiting vibration-rotational splitting. Vibration-rotational interaction lifts the AlA* degeneracy of K = 3 levels. Inversion splitting is regarded to be negligible. Due to spin statistics only one component of the inversion doublet has nonzero intensity. 0022-2852191 $3.00 Copy-@bt
0 1991 by Academic
All rights of reproduction
28 Press, Inc.
in any form resewed.
NITROGEN
19
TRIFLUORIDE
olution of approximately 300 kHz. For an absorption cell we used a l-m glass tube; the sample was used without further purification. The signals were recorded with frequency modulation at 60 kHz and 2fphase sensitive detection. In symmetric top molecules higher order vibration-rotational interaction may split the otherwise degenerate A I and A1 components of (K, 1) levels, 1being the quantum number indicating the vibrational angular momentum along the symmetry axis ( 12,
9
Nki
i
R 22,3
-I
1MHz
I-
i
FIG. 2. Series of R-branch transitions with J = 16, 22. 23. 31, and 33 with A’ = 3 splitting in the V, fundamental of NF, (R( 16.3) not resolved). Resolution of these 5 MHz scans is about 300 kHz. Frequency modulation and phase sensitive 2f detection at 60 kHz were applied. The large spike in the bottom trace is an artifact produced by the MW signal source, but greatly enhanced because more than 100 scans had been added up for this recording.
30
HijHE AND KREINER
13). In our case splitting occurs for levels with K = 3n, the effect on the K = 3 levels being dominant. The situation is similar to that for phosphine (14-16). The symmetry species A, and AZ of C,, are related to the A+ and A_ species in a way described in Ref. (16). Neglecting centrifugal distortion corrections and the resonance term which affects only the A+ component of K = 3, the splitting is given by the expression Au = {(J + K)!/(J
- K)! >a q(K, I).
(1)
As an example, Fig. 1 shows K = 3 levels of NF, in the ground and in the v1 (A,) excited state together with observed infrared transitions. We have assumed a level scheme with the A_ above the A+ levels. Figure 2 gives the K = 3 transitions on which splitting could be resolved so far. The sideband frequencies listed in Table I refer to the centers of the doublets with an error in frequency measurement of 1O-5 cm-’ or less. For each transition several recordings have been averaged. The q values derived from a fit seem to indicate a situation where the upper levels in the ground and in the excited state are connected. Assuming a crossover situation, i.e., the upper ground state level connected to the lower excited state level, leads to one of the q constants being negative. The separation of the A+A_ doublets (in kHz) and the q constants (in Hz) are given with uncertainties indicated being one standard error. Among the more than 100 saturation dips observed so far in the infrared spectrum of the v1 fundamental there were 10 transitions showing quadrupole structure, among them the P( 3, 2) transition where only the excited state is split. Examples are given in Fig. 3. The transitions P(3, 0) and P( 3, 2) had been recorded with the upper sideband of the P( 38) line in the 9 pm band of the COZ laser, the transition P( 19, 15) with the lower sideband of 9 P( 20). Using the expression for the quadrupole interaction energy
esQ{(3K2/J(J+ 1) - W-U,
J,
(2)
F),
with f( I, J, F) being Casimir’s function, we obtained the values given in Table II,
TABLE I Vibration-Rotational Transition
Laser CO2
9w
Splitting in the u, R Branch of NF,
Sideband/MHz (center
Splitting
of doublet)
obs./kHz
IXlC./kHZ
J, K R 16.3
P 22
R 22, 3
P
18
+ 14 046.980
375 (14)
374.9 (51)
R
P 16
-16 084.503
458 (26)
458.2 (57)
23.3
-14 891.592
not resolved
R
31, 3
P 10
+ 16 686.296
1740 (18)
1738.8 (70)
R
33, 3
P
+ 14 070.656
2288 (25)
2288.2 (95)
8
q (3,O) excited state
0.01229
(39) Hz
q (3,0) ground state
0.01304
(47) Hz
NITROGEN
-I
1MHr
31
TRIFLUORIDE
I-
ll
I
FIG. 3. Quadrupole splitting on the transitions P(3, O), P( 3, 2). and R( 19, 15). The range of the scans is 5 MHz. Among the more than 100 transitions in the Y, fundamental of NF, observed with saturation spectroscopy there were 10 with resolvable quadrupole hyperfine structure. In the case of the P( 3. 2) there is no splitting of the ground state level and all three components could be separated.
which are compared with the results obtained from microwave observations ( 9). Our values agree with the microwave data within the standard error which is one times r.m.s. in our case, but do not differ significantly between the ground and the excited state.
TABLE II eQq Values for NF3 in the Ground and Y, Excited State Microwave
This work MHZ ground state VI state
(Ref. 5)
7.088
(30)
- 7.07 (10)
- 7.082
(32)
____.
(Ref. 8) 7.01
(6)
6.92 (20)
32
HOHE AND KREINER ACKNOWLEDGMENT
Financial support of the Deutsche Forschungsgemeinschaft and of the Fonds der Chemischen Industrie isgratefully acknowledged. We also thank the Solvay Fhtor und Derivate GmbH/Soltronic GmbH, Hannover, for providing us with a sample of nitrogen trifluoride. RECEIVED:
June 10, 1991 REFERENCES
1. R. J. L. POPPLEWELL, F. N. MASRI,AND H. W. THOMPSON,Spectrochim. Acta Part A 23,2197-2807 (1967). 2. J. SHAMIRAND H. H. HYMAN, Spectrochim. Acta Part A 23, 1899-1901 (1967). 3. A. ALLAN,J. L. DUNCAN,J. H. HOLLOWAY,ANDD. MCKEAN, J. Mol. Spectrosc. 31,368-377 ( 1968). 4. A. C. JEANNOTTE II AND JOHNOVEREND,Spectrochim. Acta Part A 33, 1067-107 1 ( 1977). 5. J. SHERIDANAND W. GORDY, Phys. Rev. 79, 513-515 ( 1950). 6. C. M. JOHNSON,R. TRAMBARULO, AND W. GORDY, Phys. Rev. 84, 1178-l 180 ( 1951). 7. M. COWANAND W. G~RDY, Bull. Am. Phys. SOC.Ser. II 5,241 ( 1960). 8. M. OTAKE, C. MATSUMURA,AND Y. MORINO,J. Mol. Spectrosc. 28, 316-324 (1968); 28, 325-340 (1968). 9. S. N. GHOSH,R. TRAMBARULO, AND W. GORDY, J. Chem. Phys. 21,308-310 ( 1953). IO. A. M. MIRRIAND G. CAZZOLI,J. Chem. Phys. 47, 1197-l 198 ( 1967). Il. H. PRINZ,W. HOHE, W. A. KREINER,M. LOETE,J. HILICO,G. PIERRE,AND G. MAGERL,J. Mol. Spectrosc. 135, 144-160 ( 1989). 12. T. OKA, J. Chem. Phys. 47,5410-5426 (1967). 13. D. PA~~IJSEK AND M. R. ALIEV,“Molecular Vibrational/Rotational Spectra,” Academia, Prague, 1982. 14. P. B. DAVIES,R. M. NEUMANN,S. C. WOFSY, AND W. KLEMPERER, J. Chem. Phys. 55, 3564-3568 (1971). IS. S. TANIMURAAND K. TAKAGI, J. Mol. Spectrosc. 104,4 14-4 16 ( 1984). 16. G. TARRAGOAND M. DANG NHU, J. Mol. Spectrosc. 111,425-439 ( 1985).