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Rotationally resolved overtone transitions of 70GeH4 in the visible and near-infrared
Volume 192, number 4
CHEMICAL PHYSICS LETTERS
8 May 1992
Rotationally resolved overtone transitions of 70GeH4 in the visible and near-infrared A. Campargue, J. Vetterhiiffer and M. Chenevier Laboratoire de Spectromktrie Physique I, UniversitCJoseph Fourier de Grenoble, B.P. 87, 38402 Saint-Martin-d’H&res Cedex, France
Received 3 February 1992; in final form 28 February 1992
The AuocH= 6,7 and 8 overtone transitions of natural germane and of mono isotopic germane “‘GeH., have been measured with rotational resolution by intracavity laser absorption spectroscopy. The AvocH= 6 and 7 rotational structure is found to be that of a pseudo-symmetric top as expected for this molecule close to the local mode limit. On the other hand the Au,,,= 8 shows a more complicated structure which has not yet been analyzed.
1. Introduction
states vanishes and simple relationships between the reduce the rotational structure to that of a CjV symmetric-top molecule. In a recent paper [ 6 1, Lehmann has showed that this effect depends only on a separation of time scales: in a molecule which is close to local mode limit, the tunneling time between two (near degenerate) local modes is much longer than the rotational period. In consequence, the rotational structure corresponds to a slightly prolate molecule due to the total vibrational excitation localized in a single bond. In this Letter, we report the spectra of the visible high overtone transitions of germane obtained by ICLAS. The comparison of these experimental spectra with the local mode prediction is particularly interesting as the GeH, molecule is expected to be close to the local mode limit at this high vibrational energy.
Hz2 coefficients
Recently, there has been considerable interest in the rotationally resolved overtone spectroscopy of MH4 hydrides (where M=C, Si, Ge and Sn). The most striking phenomenon is that the rotational structure of overtone transitions in molecules such as silane and germane exhibits a pseudo-symmetric top structure. This effect has been predicted by Halonen and Robiette [ 1 ] in the local mode limit and observed for the first time in the AvGeH= 3 overtone transition of germane [ 2 1. The AUsiH= 3, 4 and 5 overtone bands of silane also show this pseudosymmetric top structure [ 31 while the AVsiH= 6 overtone structure, which we have observed by ICLAS [ 41 is more complicated, probably perturbed by interaction with a dark vibrational state. Another example of this feature has been observed in the first overtone transition of the “%nHq molecule which is close to local mode limit [ 5 1. The similarity between the rotational structure of the excited stretching states of MH4 molecules and that of a Cj, symmetric top molecule can be well accounted for, both in the normal mode picture [3] and in the local mode picture [ 11. At the local mode limit (as defined by Halonen and Robiette in ref. [ 1 ] ) the Coriolis effect in the stretching vibrational ’ Associated with CNRS (URA 008).
2. Experimental method The intracavity laser absorption spectroscopy (ICLAS) technique is a highly sensitive absorption technique particularly well suited to obtain visible overtone spectra (see ref. [ 7 ] for a recent review and more details ). The experimental method is based on the high sensitivity of a broadband laser to intracavity losses, e.g. absorption, due to the absorber contained in an intracavity cell. The absorption lines
0009-2614/92/$ 05.00 0 1992 Elsevier Science Publishers B.V. All rights reserved.
353
Volume 192,number4
8May1992
CHEMICALPHYSICSLETTERS
appear superimposed on the broadband spectrum of a dye laser pumped by an argon laser. The dye spectrum is time resolved and the time tg, the generation time spent from starting the dye laser to the observation of the spectrum, gives directly the equivalent absorption pathlength,
lx’ = ctg> where c is the velocity of light. In fact, this equivalent pathlength must be weighted by the occupation ratio of the cavity as the absorber occupies only a fraction of the dye laser cavity,
typically 0.02 cm-’ for the AvoeH= 7 band and 0.05 cm-’ for the Av~,~ = 6 band.
3. Results The ICLAS spectra of the AvGeH= 6 and 8 stretching overtones for “GeH4 are shown in figs. 1 and 2. The pressure and the equivalent pathlength obtained from eq. ( 1) were P= 140 Torr and le_= 5.2 km for
(1) where I is the absorption pathlength and L the total optical length of the cavity. In the present work, the absorption pathlength in the cell was 50 cm and the total length of the cavity 115 cm, which gives an equivalent pathlength of 127 10 m for a typical generation time of 100 us. The different dyes used to record the duo,” = 6, 7 and 8 spectra of germane were styryl 9, pyridine 2 and DCM, respectively. The spectral resolution of the ICLAS experiment is determined by the resolution of the grating spectrograph which disperses the spectrum. As the experiments were carried out with a typical pressure of 100 Torr of germane in the cell, the linewidths were mainly determined by collisional broadening and our highest resolving power (800000) was not needed. In consequence the spectra were recorded with a practical resolving power of 200000 which corresponds to a typical apparatus function width of 0.03 cm- ’ (hwhm ). Note that the contribution of the Doppler broadening to the linewidth is small (about 0.01 cm-‘). The absorption spectrum obtained in our experiment is in fact the superposition of the absorption spectrum of germane with that of the intracavity atmosphere. We currently use the atmospheric water vapor lines for an accurate calibration of the spectrum [ 8 1. Unfortunately the water spectrum is very sparse in the range of frequency of the three overtone bands studied here and we had to introduce an intracavity iodine cell to calibrate the Av~,~ = 7 spectrum. The accuracy on the wavenumber positions is 354
‘I
P(J) I 9
5
7
3
70GeH,
R(J)
I JO2466
v=6
I 11650
11600
11700
wavenumber
(cm-l)
Fig.I. AuGcH= 6 overtone spectrum of monoisotopic germane, “GeH,, obtained by ICLAS.The experimental pressure was 140 Torr and the equivalent indicated.
pathlength
5.2 km. The J assignment
is
1
14960
14980 wavenumber
15000
15020
(cm-l)
Fig. 2. AuoeH = 8 overtone spectrum of monoisotopic germane, “‘GeH4, obtained by ICLAS. The experimental pressure was 144 Torr and the equivalent pathlength 22.1 km. Here, the rotational structure is much more complicated and perturbed than for the AvoeH = 6 and 7 bands.
8 May 1992
CHEMICAL PHYSICS LETTERS
Volume 192, number 4
experiments, even the J periodicity was not observed. The lines corresponding to the most abundant isotopic species ( “GeH4 2 l%, 72GeH4 27% and 74GeH4 36%) are easily identified in our spectra of natural germane but the monoisotopic spectrum is, of course, much less complex but also better resolved as there is no pressure broadening due to the other isotopic species. 3.1. Vibrational analysis 13315
13310
wavenumber
13320 (cm
- 1)
Fig. 3. Expansion of the AvoeH= 7 overtone spectrum. The K labelling corresponding to the pseudo-symmetric top structure is given for each line. Some line position and intensity perturbations are noticeable. The experimental pressure was 60 Torr and the equivalent pathlength 9. I km.
Av=6, P=60 Torr and 1,,=9.1 km for Au=7 and P= 144 Torr and l,= 22.1 km for Au= 8. Fig. 3 shows an expanded section of the AvoeH= 7 overtone spectrum of monoisotopic germane. The corresponding bands of natural germane have been previously observed by intracavity photoacoustic detection [ 91 but due to the presence of the different isotopes and to the low resolution of these
The observed band origins of the different germane isotopes “GeH4, 72GeH4 and 74GeH4are listed in table 1 together with the results available in the literature. The ‘OGeH4 band origins were obtained from a preliminary rotational analysis of the spectra while the 72GeH4 and 74GeH4 band origins were deduced from the isotopic shift measured on our natural germane spectra. These data are very well fitted to the usual Morse energy level formula: AE= (CO,--w,x,)v-w,x,v2.
(2)
The Birge-Sponer fit yields the following accurate values of the harmonic frequency w, and the anharmonicity constant W,J, of the “GeH4 isotope: w,=2179.4(2)
cm-’ andw,x,=33.95(3)
cm-‘.
Table I Observed band origins (in cm- ’ ) of the three major isotopic species of germane. Uncertainties in parentheses are one standard deviation in the last figure quoted “‘GeH4 VI
(A,) b,
~3 (F2)
b’
1000 (F2) 2000 (FI) 3000 (F,) 6000 (F2) 7000 (F,) 8000 (Fj) 9000 ( F2)
‘) d, ‘) ‘) ‘) r) I)
2110.7232 2112.0345 2111.706 4155.1213 6130.4314 11650.333(6) 13356.057(9) 14996.41(8)
‘OGeH,, I a)
1 0.12 0.01
‘*GeH4
74GeH4
2110.7137 2111.5756 2111.3601 4154.4551 6129.4823 11648.74(6) 13354.33(6)
2110.7052 2111.1423 2111.0330 4153.8246 6128.5811 11647.23(6) 13352.66(6) 16574
‘) Estimated relative intensity (au). This work. b, Ref. [lo]. ‘) Band origin or the pure local mode state obtained from: EIWO=v3+ i (vi -us). d, Ref. [ll]. ‘) This work. Preliminary values obtained from the analysis of the pseudo-symmetric top rotational structure. ‘) This work. Estimated value obtained from the Q-branch origin not included in the Birge-Sponer tit. g, Ref. [ 91. Natural germane value not included in the Birge-Sponer fit.
355
Volume 192. number 4
CHEMICAL
These values lead to a root mean square deviation of 0.25 cm-’ on the energy levels. It is interesting to analyze the influence of the isotopic substitution of the germanium atom on the harmonic frequency and on the anharmonicity. The variation of these quantities from the 70GeH4 values is given in table 2 for 72GeH4 and 74GeH4. If we assume a Morse oscillator potential function for each GeH bond, these variations can be calculated using the following expressions [ 12 ] :
and Ac&‘& =w,x,
(1
-P~o/P,)
,
(3b)
where i=72 or 74 and p70 and p, are the reduced masses of the 70GeH and ‘GeH bonds, respectively. The difference between the experimental and calculated values listed in table 2 is much larger than the experimental uncertainty. We have assumed that the Morse energy level formula (eq. (2) ) corresponds to one GeH bond and taken the corresponding reduced mass in eqs. (3 ). This assumption must be correct in this molecule which is very close to local mode limit as the vibrational coupling between two bonds is very weak (see ref. [ 131 for example). In consequence, the discrepancy between experiment and theory reflects either the deviation of the true stretching potential from the Morse potential function or the occurrence of local perturbations such as Fermi resonance with some other vibrational states.
PHYSICS
LETTERS
8 May I992
from the analysis of a well isolated line of the Au= 6 overtone spectrum. The pseudo-symmetric top structure of the Avoe~ = 6 overtone band is clearly apparent and the lines corresponding to K, multiple of 3 are more intense as expected. However, some intensity and position perturbations are observed. As shown in fig. 3, the rotational structure of the AVC,H= 7 transition is even closer to a symmetric top parallel band and a preliminary analysis has shown that the (J, K) assignment of more than sixty lines is straightforward. On the other hand, the rotational structure of the Avoeu = 8 transition is severely perturbed as shown in fig. 2. No well formed symmetric top pattern is observed. The rotational analysis of the three bands is in progress and will be published with the line positions separately. Acknowledgement We thank Professor Hans Burger versity of Wuppertal, Anorganische synthesis of monoisotopic germane helpful discussions. We also thank gorov for useful discussions.
from the UniChemie, for the 70GeH4 and for Dmitri Permo-
References [ I] L. Halonen and A.G. Robiette, J. Chem. Phys. 84 ( 1986) 6861.
[ 21 Q. Zhu, B.A. Thrush and A.G. Robiette, Chem. Phys. Letters 150 (1988)
181.
[ 31 Q. Zhu, B. Zhang, Y. Ma and H. Qian, Chem. Phys. Letters 3.2. Rotational analysis
164 (1989)
596. M. Chenevier and F. Stoeckel, Chem. Phys. 138 (1989) 405. M. Halonen, L. Halonen, H. Burger and S. Sommer, J. Chem. Phys. 93 ( 1990) 1607. K.K. Lehmann, J. Chem. Phys. 95 ( 1991) 236 1. A. Campargue, F. Stoeckel and M. Chenevier, Spectrochim. Acta Rev. 13 ( 1990) 69. J.Y. Mandin, J.P. Chevillard, C. Camy-Peret, J.M. Flaud and J.W. Brault, J. Mol. Spectry. 116 ( 1986) 167. R.A. Bernheim, D.C. Albee, F.W. Lampe, J.F. O’Keefe and J.R. Qualey III, J. Phys. Chem. 92 (1988) 1850. S.Q. Mao, R. Saint-Loup, A. Aboumajd, P. Lepage, H. Burger and A.G. Robiette, J. Raman Spectry. 13 ( 1982) 257.
[ 41 A. Campargue, The different spectra are rotationally resolved and the J assignment is straightforward for the Au= 6 and 7 bands. Note that the pressure broadening coeffcient has been estimated to be 0.2 cm-‘/atm (fwhm)
[ 51 [ 61 [ 71 [8]
Table 2 Experimental and calculated values of the isotopic harmonic frequency w, and the anharmonicity w&
shift of the
[ 91 [ IO]
v(70GeH,)-v(‘4GeH4)
Am. A&&
356
u(“GeH4)-v(“GeH4)
exp.
talc.
exp.
talc.
0.74(4) 0.0318(8)
0.829 0.0258
0.378(4) 0.0162( 1)
0.406 0.0133
[ 111 Q. Zhu, H. Qian and B.A. Thrush, Chem. Phys. Letters 186 (1991) 436. [ 121 J.M. Hollas, High resolution spectroscopy (Butterworth, London, 1982). [ 131 L. Halonen and M.S. Chad, Mol. Phys. 46 (1982) 239.
CHEMICAL PHYSICS LETTERS
8 May 1992
Rotationally resolved overtone transitions of 70GeH4 in the visible and near-infrared A. Campargue, J. Vetterhiiffer and M. Chenevier Laboratoire de Spectromktrie Physique I, UniversitCJoseph Fourier de Grenoble, B.P. 87, 38402 Saint-Martin-d’H&res Cedex, France
Received 3 February 1992; in final form 28 February 1992
The AuocH= 6,7 and 8 overtone transitions of natural germane and of mono isotopic germane “‘GeH., have been measured with rotational resolution by intracavity laser absorption spectroscopy. The AvocH= 6 and 7 rotational structure is found to be that of a pseudo-symmetric top as expected for this molecule close to the local mode limit. On the other hand the Au,,,= 8 shows a more complicated structure which has not yet been analyzed.
1. Introduction
states vanishes and simple relationships between the reduce the rotational structure to that of a CjV symmetric-top molecule. In a recent paper [ 6 1, Lehmann has showed that this effect depends only on a separation of time scales: in a molecule which is close to local mode limit, the tunneling time between two (near degenerate) local modes is much longer than the rotational period. In consequence, the rotational structure corresponds to a slightly prolate molecule due to the total vibrational excitation localized in a single bond. In this Letter, we report the spectra of the visible high overtone transitions of germane obtained by ICLAS. The comparison of these experimental spectra with the local mode prediction is particularly interesting as the GeH, molecule is expected to be close to the local mode limit at this high vibrational energy.
Hz2 coefficients
Recently, there has been considerable interest in the rotationally resolved overtone spectroscopy of MH4 hydrides (where M=C, Si, Ge and Sn). The most striking phenomenon is that the rotational structure of overtone transitions in molecules such as silane and germane exhibits a pseudo-symmetric top structure. This effect has been predicted by Halonen and Robiette [ 1 ] in the local mode limit and observed for the first time in the AvGeH= 3 overtone transition of germane [ 2 1. The AUsiH= 3, 4 and 5 overtone bands of silane also show this pseudosymmetric top structure [ 31 while the AVsiH= 6 overtone structure, which we have observed by ICLAS [ 41 is more complicated, probably perturbed by interaction with a dark vibrational state. Another example of this feature has been observed in the first overtone transition of the “%nHq molecule which is close to local mode limit [ 5 1. The similarity between the rotational structure of the excited stretching states of MH4 molecules and that of a Cj, symmetric top molecule can be well accounted for, both in the normal mode picture [3] and in the local mode picture [ 11. At the local mode limit (as defined by Halonen and Robiette in ref. [ 1 ] ) the Coriolis effect in the stretching vibrational ’ Associated with CNRS (URA 008).
2. Experimental method The intracavity laser absorption spectroscopy (ICLAS) technique is a highly sensitive absorption technique particularly well suited to obtain visible overtone spectra (see ref. [ 7 ] for a recent review and more details ). The experimental method is based on the high sensitivity of a broadband laser to intracavity losses, e.g. absorption, due to the absorber contained in an intracavity cell. The absorption lines
0009-2614/92/$ 05.00 0 1992 Elsevier Science Publishers B.V. All rights reserved.
353
Volume 192,number4
8May1992
CHEMICALPHYSICSLETTERS
appear superimposed on the broadband spectrum of a dye laser pumped by an argon laser. The dye spectrum is time resolved and the time tg, the generation time spent from starting the dye laser to the observation of the spectrum, gives directly the equivalent absorption pathlength,
lx’ = ctg> where c is the velocity of light. In fact, this equivalent pathlength must be weighted by the occupation ratio of the cavity as the absorber occupies only a fraction of the dye laser cavity,
typically 0.02 cm-’ for the AvoeH= 7 band and 0.05 cm-’ for the Av~,~ = 6 band.
3. Results The ICLAS spectra of the AvGeH= 6 and 8 stretching overtones for “GeH4 are shown in figs. 1 and 2. The pressure and the equivalent pathlength obtained from eq. ( 1) were P= 140 Torr and le_= 5.2 km for
(1) where I is the absorption pathlength and L the total optical length of the cavity. In the present work, the absorption pathlength in the cell was 50 cm and the total length of the cavity 115 cm, which gives an equivalent pathlength of 127 10 m for a typical generation time of 100 us. The different dyes used to record the duo,” = 6, 7 and 8 spectra of germane were styryl 9, pyridine 2 and DCM, respectively. The spectral resolution of the ICLAS experiment is determined by the resolution of the grating spectrograph which disperses the spectrum. As the experiments were carried out with a typical pressure of 100 Torr of germane in the cell, the linewidths were mainly determined by collisional broadening and our highest resolving power (800000) was not needed. In consequence the spectra were recorded with a practical resolving power of 200000 which corresponds to a typical apparatus function width of 0.03 cm- ’ (hwhm ). Note that the contribution of the Doppler broadening to the linewidth is small (about 0.01 cm-‘). The absorption spectrum obtained in our experiment is in fact the superposition of the absorption spectrum of germane with that of the intracavity atmosphere. We currently use the atmospheric water vapor lines for an accurate calibration of the spectrum [ 8 1. Unfortunately the water spectrum is very sparse in the range of frequency of the three overtone bands studied here and we had to introduce an intracavity iodine cell to calibrate the Av~,~ = 7 spectrum. The accuracy on the wavenumber positions is 354
‘I
P(J) I 9
5
7
3
70GeH,
R(J)
I JO2466
v=6
I 11650
11600
11700
wavenumber
(cm-l)
Fig.I. AuGcH= 6 overtone spectrum of monoisotopic germane, “GeH,, obtained by ICLAS.The experimental pressure was 140 Torr and the equivalent indicated.
pathlength
5.2 km. The J assignment
is
1
14960
14980 wavenumber
15000
15020
(cm-l)
Fig. 2. AuoeH = 8 overtone spectrum of monoisotopic germane, “‘GeH4, obtained by ICLAS. The experimental pressure was 144 Torr and the equivalent pathlength 22.1 km. Here, the rotational structure is much more complicated and perturbed than for the AvoeH = 6 and 7 bands.
8 May 1992
CHEMICAL PHYSICS LETTERS
Volume 192, number 4
experiments, even the J periodicity was not observed. The lines corresponding to the most abundant isotopic species ( “GeH4 2 l%, 72GeH4 27% and 74GeH4 36%) are easily identified in our spectra of natural germane but the monoisotopic spectrum is, of course, much less complex but also better resolved as there is no pressure broadening due to the other isotopic species. 3.1. Vibrational analysis 13315
13310
wavenumber
13320 (cm
- 1)
Fig. 3. Expansion of the AvoeH= 7 overtone spectrum. The K labelling corresponding to the pseudo-symmetric top structure is given for each line. Some line position and intensity perturbations are noticeable. The experimental pressure was 60 Torr and the equivalent pathlength 9. I km.
Av=6, P=60 Torr and 1,,=9.1 km for Au=7 and P= 144 Torr and l,= 22.1 km for Au= 8. Fig. 3 shows an expanded section of the AvoeH= 7 overtone spectrum of monoisotopic germane. The corresponding bands of natural germane have been previously observed by intracavity photoacoustic detection [ 91 but due to the presence of the different isotopes and to the low resolution of these
The observed band origins of the different germane isotopes “GeH4, 72GeH4 and 74GeH4are listed in table 1 together with the results available in the literature. The ‘OGeH4 band origins were obtained from a preliminary rotational analysis of the spectra while the 72GeH4 and 74GeH4 band origins were deduced from the isotopic shift measured on our natural germane spectra. These data are very well fitted to the usual Morse energy level formula: AE= (CO,--w,x,)v-w,x,v2.
(2)
The Birge-Sponer fit yields the following accurate values of the harmonic frequency w, and the anharmonicity constant W,J, of the “GeH4 isotope: w,=2179.4(2)
cm-’ andw,x,=33.95(3)
cm-‘.
Table I Observed band origins (in cm- ’ ) of the three major isotopic species of germane. Uncertainties in parentheses are one standard deviation in the last figure quoted “‘GeH4 VI
(A,) b,
~3 (F2)
b’
1000 (F2) 2000 (FI) 3000 (F,) 6000 (F2) 7000 (F,) 8000 (Fj) 9000 ( F2)
‘) d, ‘) ‘) ‘) r) I)
2110.7232 2112.0345 2111.706 4155.1213 6130.4314 11650.333(6) 13356.057(9) 14996.41(8)
‘OGeH,, I a)
1 0.12 0.01
‘*GeH4
74GeH4
2110.7137 2111.5756 2111.3601 4154.4551 6129.4823 11648.74(6) 13354.33(6)
2110.7052 2111.1423 2111.0330 4153.8246 6128.5811 11647.23(6) 13352.66(6) 16574
‘) Estimated relative intensity (au). This work. b, Ref. [lo]. ‘) Band origin or the pure local mode state obtained from: EIWO=v3+ i (vi -us). d, Ref. [ll]. ‘) This work. Preliminary values obtained from the analysis of the pseudo-symmetric top rotational structure. ‘) This work. Estimated value obtained from the Q-branch origin not included in the Birge-Sponer tit. g, Ref. [ 91. Natural germane value not included in the Birge-Sponer fit.
355
Volume 192. number 4
CHEMICAL
These values lead to a root mean square deviation of 0.25 cm-’ on the energy levels. It is interesting to analyze the influence of the isotopic substitution of the germanium atom on the harmonic frequency and on the anharmonicity. The variation of these quantities from the 70GeH4 values is given in table 2 for 72GeH4 and 74GeH4. If we assume a Morse oscillator potential function for each GeH bond, these variations can be calculated using the following expressions [ 12 ] :
and Ac&‘& =w,x,
(1
-P~o/P,)
,
(3b)
where i=72 or 74 and p70 and p, are the reduced masses of the 70GeH and ‘GeH bonds, respectively. The difference between the experimental and calculated values listed in table 2 is much larger than the experimental uncertainty. We have assumed that the Morse energy level formula (eq. (2) ) corresponds to one GeH bond and taken the corresponding reduced mass in eqs. (3 ). This assumption must be correct in this molecule which is very close to local mode limit as the vibrational coupling between two bonds is very weak (see ref. [ 131 for example). In consequence, the discrepancy between experiment and theory reflects either the deviation of the true stretching potential from the Morse potential function or the occurrence of local perturbations such as Fermi resonance with some other vibrational states.
PHYSICS
LETTERS
8 May I992
from the analysis of a well isolated line of the Au= 6 overtone spectrum. The pseudo-symmetric top structure of the Avoe~ = 6 overtone band is clearly apparent and the lines corresponding to K, multiple of 3 are more intense as expected. However, some intensity and position perturbations are observed. As shown in fig. 3, the rotational structure of the AVC,H= 7 transition is even closer to a symmetric top parallel band and a preliminary analysis has shown that the (J, K) assignment of more than sixty lines is straightforward. On the other hand, the rotational structure of the Avoeu = 8 transition is severely perturbed as shown in fig. 2. No well formed symmetric top pattern is observed. The rotational analysis of the three bands is in progress and will be published with the line positions separately. Acknowledgement We thank Professor Hans Burger versity of Wuppertal, Anorganische synthesis of monoisotopic germane helpful discussions. We also thank gorov for useful discussions.
from the UniChemie, for the 70GeH4 and for Dmitri Permo-
References [ I] L. Halonen and A.G. Robiette, J. Chem. Phys. 84 ( 1986) 6861.
[ 21 Q. Zhu, B.A. Thrush and A.G. Robiette, Chem. Phys. Letters 150 (1988)
181.
[ 31 Q. Zhu, B. Zhang, Y. Ma and H. Qian, Chem. Phys. Letters 3.2. Rotational analysis
164 (1989)
596. M. Chenevier and F. Stoeckel, Chem. Phys. 138 (1989) 405. M. Halonen, L. Halonen, H. Burger and S. Sommer, J. Chem. Phys. 93 ( 1990) 1607. K.K. Lehmann, J. Chem. Phys. 95 ( 1991) 236 1. A. Campargue, F. Stoeckel and M. Chenevier, Spectrochim. Acta Rev. 13 ( 1990) 69. J.Y. Mandin, J.P. Chevillard, C. Camy-Peret, J.M. Flaud and J.W. Brault, J. Mol. Spectry. 116 ( 1986) 167. R.A. Bernheim, D.C. Albee, F.W. Lampe, J.F. O’Keefe and J.R. Qualey III, J. Phys. Chem. 92 (1988) 1850. S.Q. Mao, R. Saint-Loup, A. Aboumajd, P. Lepage, H. Burger and A.G. Robiette, J. Raman Spectry. 13 ( 1982) 257.
[ 41 A. Campargue, The different spectra are rotationally resolved and the J assignment is straightforward for the Au= 6 and 7 bands. Note that the pressure broadening coeffcient has been estimated to be 0.2 cm-‘/atm (fwhm)
[ 51 [ 61 [ 71 [8]
Table 2 Experimental and calculated values of the isotopic harmonic frequency w, and the anharmonicity w&
shift of the
[ 91 [ IO]
v(70GeH,)-v(‘4GeH4)
Am. A&&
356
u(“GeH4)-v(“GeH4)
exp.
talc.
exp.
talc.
0.74(4) 0.0318(8)
0.829 0.0258
0.378(4) 0.0162( 1)
0.406 0.0133
[ 111 Q. Zhu, H. Qian and B.A. Thrush, Chem. Phys. Letters 186 (1991) 436. [ 121 J.M. Hollas, High resolution spectroscopy (Butterworth, London, 1982). [ 131 L. Halonen and M.S. Chad, Mol. Phys. 46 (1982) 239.