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Microwave Spectrum, Quadrupole Coupling Constants, and Dipole Moment of Oxiranecarbonitrile
JOURNAL OF MOLECULAR SPECTROSCOPY ARTICLE NO.
179, 61–64 (1996)
0183
Microwave Spectrum, Quadrupole Coupling Constants, and Dipole Moment of Oxiranecarbonitrile F. Mu¨ller and A. Bauder Laboratorium fu¨r Physikalische Chemie, Eidgeno¨ssische Technische Hochschule, CH-8092 Zu¨rich, Switzerland Received February 9, 1996; in revised form April 24, 1996
The rotational spectrum of oxiranecarbonitrile has been measured between 8 and 40 GHz with a Stark spectrometer and a waveguide Fourier transform microwave spectrometer. Three rotational constants, five centrifugal distortion constants, and the diagonal elements of the 14N quadrupole coupling tensor were fitted to the observed transition frequencies. All three components of the electric dipole moment were determined from Stark effect measurements. q 1996 Academic Press, Inc.
sources in the frequency range from 8 to 40 GHz. The sample was contained in a 4-m-long Stark cell of our own design and a frequency of 30 kHz was used for the square-wave modulation. The spectrometer was operated under control of a personal computer for the detailed recording of individual transitions. Accurate center frequencies of rotational transitions were interpolated from digital sweeps with step sizes of 10 kHz. The frequency averaged from sweeps in both directions was estimated to be accurate within 30 kHz.
I. INTRODUCTION
The three-membered ring molecule oxiranecarbonitrile (C3H3NO) is a CN-substituted derivative of oxirane (ethylene oxide). The oxirane ring is a rather rigid system possessing no low-frequency normal vibrations. A single substitution destroys the symmetry of oxirane and gives rise to two enantiomeric forms. All three components of the permanent electric dipole moment are present in the absence of symmetry. The rotational spectra of a number of different fluorosubstituted oxiranes have been reported (1–4) but no singly halogen-substituted oxirane was among them. Oxiranecarbonitrile has been suggested to be an important prebiologic precursor for the formation of biological molecules (5–7). Interest developed over whether this molecule is present in interstellar clouds in detectable concentrations. Identification in interstellar clouds requires knowledge of accurate rotational and centrifugal distortion constants as well as the permanent electric dipole moment of oxiranecarbonitrile. We report here the measurement and analysis of the microwave spectrum of oxiranecarbonitrile over the range of 8–40 GHz. The observed transitions were assigned from broadband sweeps with a Stark spectrometer and were used to determine the rotational and centrifugal distortion constants. The technique of pulsed Fourier transform microwave (FTMW) spectroscopy was applied to resolve the hyperfine splitting due to the 14N nucleus in oxiranecarbonitrile and led to the quadrupole coupling constants. The components of the permanent electric dipole moment were determined from FTMW Stark experiments. A report of the search for interstellar oxiranecarbonitrile will be published elsewhere (8).
(b) Fourier Transform Microwave Spectrometer The FTMW spectrometer of the Ekkers–Flygare type (9) offered higher resolution than the Stark spectrometer. Details of the design of our spectrometer were given elsewhere (10). Only a brief description of the operating conditions is repeated here. Microwave pulses of 50 ns duration and a peak power of 17 W polarized the sample in a 6-m-long waveguide cell for the range of 12–18 GHz. The transient molecular emission signal was amplified and down-converted to the frequency range of 0–10 MHz. The signal was digitized at a rate of 20 MHz and stored in a homebuilt transient analyzer with 512 channels. The pulses were repeated at a rate of 25 kHz. To attain good signal-to-noise ratios, between 10 1 10 6 and 50 1 10 6 pulse responses were added, corresponding to measurement times between 7 and 35 min. After a Fourier transformation, the power spectrum was recovered over a range of 10 MHz with 256 points. Peak frequencies of transitions were obtained by fitting a Lorentzian to the time-domain signals. The experimental uncertainty of a peak frequency was estimated to be about 10 kHz. For the Stark effect measurements, the P-band waveguide cell of the FTMW spectrometer was replaced by a Stark cell as described previously (11, 12). For these experiments, the molecular emission signal was amplified and down-converted to the range 0–50 MHz and the pulses were repeated at 55 kHz. The experimental uncertainty of a peak frequency
II. EXPERIMENTAL DETAILS
(a) Stark Spectrometer The conventional Stark spectrometer was equipped with phased-locked backward-wave oscillators as radiation 61
0022-2852/96 $18.00 Copyright q 1996 by Academic Press, Inc. All rights of reproduction in any form reserved.
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07-09-96 13:25:55
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AP: Mol Spec
62
¨ LLER AND BAUDER MU
TABLE 1 Observed Rotational Transitions (MHz) of Oxiranecarbonitrile in the Vibrational Ground State
TABLE 2 Rotational Constants (MHz), Centrifugal Distortion Constants (kHz), and Correlation Coefficients of Oxiranecarbonitrile in the Vibrational Ground State a
was increased here to 30 kHz because of the larger channel separation. Static Stark fields up to 950 V cm01 were applied to the sample. The electric field was calibrated with the J Å 0 R 1 transition of OCS using the dipole moment of 0.71519(3) D measured by Reinartz and Dymanus (13). A sample of racemic oxiranecarbonitrile was obtained from Dr. S. Pitsch (6, 7) and used as received. Measurements with the Stark spectrometer were made at pressures of 4 Pa and power levels of 0.7 mW with the Stark cell cooled to 0207C. A lower pressure around 0.5 Pa was required for the FTMW measurements. The Stark effect was observed with the cell at room temperature. III. SPECTRAL ANALYSIS AND RESULTS
(a) Rotational Constants and Centrifugal Distortion Constants An initial set of rotational constants of oxiranecarbonitrile was calculated from the geometry of ethylene oxide (14) and acetonitrile (15). The microwave spectrum was then predicted from the initial rotational constants. Transitions were expected from all three components of the electric dipole moment. The intense J(2, J 0 1) R J(1, J 0 1) Qbranch series was first identified. The correct J assignment of individual Q-branch transitions in this series was obtained from plotting the transition frequencies in a diagram of (A 0 C )/2 versus the asymmetry parameter k (16). If the proper assignment was found, the parameters (A 0 C )/2 and k were defined from a well-defined intersection of the curves representing the measured frequencies of transitions. Further Q-branch transitions were identified subsequently from the known parameters. The independent determination of all three rotational constants required the measurement of Copyright q 1996 by Academic Press, Inc.
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JMS 7053
/
6t0d$$$201
07-09-96 13:25:55
mspal
AP: Mol Spec
MICROWAVE SPECTRUM OF OXIRANECARBONITRILE
TABLE 3 Resolved Quadrupole Components (MHz) of Rotational Transitions of Oxiranecarbonitrile in the Vibrational Ground State
63
TABLE 4 Diagonal 14N Quadrupole Coupling Constants and Correlation Coefficients of Oxiranecarbonitrile in the Vibrational Ground State a
nuclear quadrupole coupling constants of oxiranecarbonitrile were estimated when the quadrupole coupling tensor of cyclopropyl cyanide (19) was transformed to the principal axes of oxiranecarbonitrile. The assignments of the hyperfine splittings of rotational transitions followed directly from this estimate. The measured frequencies of the quadrupole components are listed in Table 3. The small splittings allowed the fitting of only two diagonal quadrupole coupling constants of the traceless tensor. The measured splittings were not TABLE 5 Stark Slopes (Hz V 02 cm2 ) and Electric Dipole Moment (D) of Oxiranecarbonitrile a
at least one R-branch transition. A few R-branch transitions were assigned from microwave–microwave double-resonance experiments (17). A suitable transition of the assigned Q-branch was pumped while searching for an R-branch transition which had a common energy level with the Q-branch transition. The accurately measured frequencies of the finally assigned transitions are listed in Table 1. Three rotational constants and five quartic centrifugal distortion constants were fitted simultaneously to the measured transition frequencies. The centrifugal distortion constants are defined according to Watson’s asymmetric reduction in the prolate I r-representation (18). The results of the leastsquares fit are collected in Table 2 with uncertainties given in parentheses as one standard deviation. (b) Quadrupole Coupling Constants In order to determine the quadrupole coupling constants due to the 14N nucleus accurately, some low J transitions were measured with the FTMW spectrometer. Preliminary Copyright q 1996 by Academic Press, Inc.
AID
JMS 7053
/
6t0d$$$201
07-09-96 13:25:55
mspal
AP: Mol Spec
64
¨ LLER AND BAUDER MU
TABLE 6 Main Quadrupole Coupling Constant xzz (MHz) in the Bond Direction for Different Nitriles
quadrupole coupling constants were transformed to the bond axis system of the CN group. The transformation was based on an assumed structure with parameters transferred from ethylene oxide (14) and acetonitrile (15). The result for the main quadrupole coupling constant xzz along the CN bond direction is compared in Table 6 to values found in related compounds. The slightly larger value outside the range of the other compounds is not significant in view of the assumed molecular structure. Finally all three components of the permanent electric dipole moment were obtained in the principal axis system from quantitative Stark effect measurements. ACKNOWLEDGMENTS Financial support by the Schweizerischer Nationalfonds (Project 20.33367.92) is gratefully acknowledged. We thank Professor A. Eschenmoser, Professor W. M. Irvine, and Professor G. Arrhenius for stimulating discussions and their interest in the present work. We are indepted to Dr. S. Pitsch for the preparation of a sample of oxiranecarbonitrile.
dependent on the nondiagonal elements. The rotational and the five centrifugal distortion constants were kept fixed at the values of Table 2 during the least-squares fit of the quadrupole coupling constants. The results are given in Table 4 together with the standard deviations in parentheses. (c) Dipole Moment Rotational transitions which showed no resolvable quadrupole splittings were selected for the determination of the electric dipole moment. The Stark effects of four rotational transitions were observed at seven to nine different dc voltages with the FTMW spectrometer equipped with a Stark cell. A regression analysis of the frequency shifts as a function of the applied static electric field verified that each individual M component had a purely quadratic Stark effect. The slopes of the M components determined the dipole moment in a weighted least-squares fit. The necessary Stark coefficients were calculated with second-order pertubation theory (20). The measured slopes are compared to the calculated slopes in Table 5 where the results of the ma , mb , and mc components of the electric dipole moment are collected from the least-squares fit. IV. CONCLUSIONS
The microwave spectrum of oxiranecarbonitrile was observed and 121 rotational transitions were assigned for the ground vibrational state. No transitions in excited vibrational states were identified. This fact demonstrates the rigid framework of the three-membered ring with no low-frequency normal vibrations. Accurate rotational and centrifugal distortion constants were fitted to the measured transition frequencies. The intensities of the rotational transitions should be sufficient for the observation of 13C and 15N isotopomers in natural abundance with modern Fourier transform microwave spectrometers. 14N nuclear hyperfine splittings were resolved for a few transitions from which the diagonal quadrupole coupling constants were determined. The obtained
REFERENCES 1. C. W. Gillies, J. Mol. Spectrosc. 71, 85–100 (1978). 2. J. W. Agopovich, J. Alexander, C. W. Gillies, and T. T. Raw, J. Am. Chem. Soc. 106, 2250–2254 (1984). 3. G. La Brecque, C. W. Gillies, and T. T. Raw, J. Am. Chem. Soc. 106, 6171–6175 (1984). 4. T. T. Raw and C. G. Gillies, J. Mol. Spectrosc. 128, 195–205 (1988). 5. A. Eschenmoser and E. Loewenthal, Chem. Soc. Rev. 21, 1–16 (1992). 6. S. Pitsch, E. Pombo-Villar, and A. Eschenmoser, Helv. Chim. Acta 77, 2251–2285 (1994). 7. S. Pitsch, Ph.D. thesis, Eidgeno¨ssische Technische Hochschule, Zu¨rich, Switzerland, 1993. 8. J. E. Dickens, W. M. Irvine, M. Ohishi, F. Mu¨ller, A. Bauder, G. Arrhenius, and A. Eschenmoser, Origins of Life and Evolution of the Biosphere, in press. 9. J. Ekkers and W. H. Flygare, Rev. Sci. Instrum. 47, 448–454 (1976). 10. A. Bauder, in ‘‘Vibrational Spectra and Structure’’ (J. R. Durig, Ed.), Vol. 20, pp. 157–188, Elsevier, New York/Amsterdam, 1993. 11. B. Vogelsanger and A. Bauder, J. Chem. Phys. 87, 4465–4470 (1987). 12. B. Vogelsanger and A. Bauder, J. Mol. Spectrosc. 130, 249–257 (1988). 13. J. M. L. J. Reinartz and A. Dymanus, Chem. Phys. Lett. 24, 346–351 (1974). 14. C. Hirose, Bull. Chem. Soc. Jpn. 47, 1311–1318 (1974). 15. K. Karakida, T. Fukuyama, and K. Kuchitsu, Bull. Chem. Soc. Jpn. 47, 299–304 (1974). 16. W. Gordy and R. L. Cook, ‘‘Microwave Molecular Spectra,’’ Chap. VII, pp. 271–272, Wiley, New York, 1984. 17. J. Ekkers, A. Bauder, and Hs. H. Gu¨nthard, J. Phys. E: Sci. Instrum. 8, 819–822 (1975). 18. J. K. G. Watson, in ‘‘Vibrational Spectra and Structure’’ (J. R. Durig, Ed.), Vol. 6, pp. 1–89, Elsevier, New York/Amsterdam, 1977. 19. O. Bo¨ttcher, N. Heineking, and D. H. Sutter, Z. Naturforsch. A 44, 655–658 (1989). 20. S. Golden and E. B. Wilson, Jr., J. Chem. Phys. 16, 669–685 (1948). 21. R. A. Creswell, G. Winnewisser, and M. C. L. Gerry, J. Mol. Spectrosc. 65, 420–429 (1977). 22. S. G. Kukolich, J. Chem. Phys. 76, 97–101 (1982). 23. E. Fliege and H. Dreizler, Z. Naturforsch. A 41, 1307–1310 (1986). 24. M. Stolze and D. H. Sutter, Z. Naturforsch. A 40, 998–1010 (1985). 25. K. Vormann, U. Andresen, N. Heineking, and H. Dreizler, Z. Naturforsch. A 43, 283–284 (1988).
Copyright q 1996 by Academic Press, Inc.
AID
JMS 7053
/
6t0d$$$201
07-09-96 13:25:55
mspal
AP: Mol Spec
179, 61–64 (1996)
0183
Microwave Spectrum, Quadrupole Coupling Constants, and Dipole Moment of Oxiranecarbonitrile F. Mu¨ller and A. Bauder Laboratorium fu¨r Physikalische Chemie, Eidgeno¨ssische Technische Hochschule, CH-8092 Zu¨rich, Switzerland Received February 9, 1996; in revised form April 24, 1996
The rotational spectrum of oxiranecarbonitrile has been measured between 8 and 40 GHz with a Stark spectrometer and a waveguide Fourier transform microwave spectrometer. Three rotational constants, five centrifugal distortion constants, and the diagonal elements of the 14N quadrupole coupling tensor were fitted to the observed transition frequencies. All three components of the electric dipole moment were determined from Stark effect measurements. q 1996 Academic Press, Inc.
sources in the frequency range from 8 to 40 GHz. The sample was contained in a 4-m-long Stark cell of our own design and a frequency of 30 kHz was used for the square-wave modulation. The spectrometer was operated under control of a personal computer for the detailed recording of individual transitions. Accurate center frequencies of rotational transitions were interpolated from digital sweeps with step sizes of 10 kHz. The frequency averaged from sweeps in both directions was estimated to be accurate within 30 kHz.
I. INTRODUCTION
The three-membered ring molecule oxiranecarbonitrile (C3H3NO) is a CN-substituted derivative of oxirane (ethylene oxide). The oxirane ring is a rather rigid system possessing no low-frequency normal vibrations. A single substitution destroys the symmetry of oxirane and gives rise to two enantiomeric forms. All three components of the permanent electric dipole moment are present in the absence of symmetry. The rotational spectra of a number of different fluorosubstituted oxiranes have been reported (1–4) but no singly halogen-substituted oxirane was among them. Oxiranecarbonitrile has been suggested to be an important prebiologic precursor for the formation of biological molecules (5–7). Interest developed over whether this molecule is present in interstellar clouds in detectable concentrations. Identification in interstellar clouds requires knowledge of accurate rotational and centrifugal distortion constants as well as the permanent electric dipole moment of oxiranecarbonitrile. We report here the measurement and analysis of the microwave spectrum of oxiranecarbonitrile over the range of 8–40 GHz. The observed transitions were assigned from broadband sweeps with a Stark spectrometer and were used to determine the rotational and centrifugal distortion constants. The technique of pulsed Fourier transform microwave (FTMW) spectroscopy was applied to resolve the hyperfine splitting due to the 14N nucleus in oxiranecarbonitrile and led to the quadrupole coupling constants. The components of the permanent electric dipole moment were determined from FTMW Stark experiments. A report of the search for interstellar oxiranecarbonitrile will be published elsewhere (8).
(b) Fourier Transform Microwave Spectrometer The FTMW spectrometer of the Ekkers–Flygare type (9) offered higher resolution than the Stark spectrometer. Details of the design of our spectrometer were given elsewhere (10). Only a brief description of the operating conditions is repeated here. Microwave pulses of 50 ns duration and a peak power of 17 W polarized the sample in a 6-m-long waveguide cell for the range of 12–18 GHz. The transient molecular emission signal was amplified and down-converted to the frequency range of 0–10 MHz. The signal was digitized at a rate of 20 MHz and stored in a homebuilt transient analyzer with 512 channels. The pulses were repeated at a rate of 25 kHz. To attain good signal-to-noise ratios, between 10 1 10 6 and 50 1 10 6 pulse responses were added, corresponding to measurement times between 7 and 35 min. After a Fourier transformation, the power spectrum was recovered over a range of 10 MHz with 256 points. Peak frequencies of transitions were obtained by fitting a Lorentzian to the time-domain signals. The experimental uncertainty of a peak frequency was estimated to be about 10 kHz. For the Stark effect measurements, the P-band waveguide cell of the FTMW spectrometer was replaced by a Stark cell as described previously (11, 12). For these experiments, the molecular emission signal was amplified and down-converted to the range 0–50 MHz and the pulses were repeated at 55 kHz. The experimental uncertainty of a peak frequency
II. EXPERIMENTAL DETAILS
(a) Stark Spectrometer The conventional Stark spectrometer was equipped with phased-locked backward-wave oscillators as radiation 61
0022-2852/96 $18.00 Copyright q 1996 by Academic Press, Inc. All rights of reproduction in any form reserved.
AID
JMS 7053
/
6t0d$$$201
07-09-96 13:25:55
mspal
AP: Mol Spec
62
¨ LLER AND BAUDER MU
TABLE 1 Observed Rotational Transitions (MHz) of Oxiranecarbonitrile in the Vibrational Ground State
TABLE 2 Rotational Constants (MHz), Centrifugal Distortion Constants (kHz), and Correlation Coefficients of Oxiranecarbonitrile in the Vibrational Ground State a
was increased here to 30 kHz because of the larger channel separation. Static Stark fields up to 950 V cm01 were applied to the sample. The electric field was calibrated with the J Å 0 R 1 transition of OCS using the dipole moment of 0.71519(3) D measured by Reinartz and Dymanus (13). A sample of racemic oxiranecarbonitrile was obtained from Dr. S. Pitsch (6, 7) and used as received. Measurements with the Stark spectrometer were made at pressures of 4 Pa and power levels of 0.7 mW with the Stark cell cooled to 0207C. A lower pressure around 0.5 Pa was required for the FTMW measurements. The Stark effect was observed with the cell at room temperature. III. SPECTRAL ANALYSIS AND RESULTS
(a) Rotational Constants and Centrifugal Distortion Constants An initial set of rotational constants of oxiranecarbonitrile was calculated from the geometry of ethylene oxide (14) and acetonitrile (15). The microwave spectrum was then predicted from the initial rotational constants. Transitions were expected from all three components of the electric dipole moment. The intense J(2, J 0 1) R J(1, J 0 1) Qbranch series was first identified. The correct J assignment of individual Q-branch transitions in this series was obtained from plotting the transition frequencies in a diagram of (A 0 C )/2 versus the asymmetry parameter k (16). If the proper assignment was found, the parameters (A 0 C )/2 and k were defined from a well-defined intersection of the curves representing the measured frequencies of transitions. Further Q-branch transitions were identified subsequently from the known parameters. The independent determination of all three rotational constants required the measurement of Copyright q 1996 by Academic Press, Inc.
AID
JMS 7053
/
6t0d$$$201
07-09-96 13:25:55
mspal
AP: Mol Spec
MICROWAVE SPECTRUM OF OXIRANECARBONITRILE
TABLE 3 Resolved Quadrupole Components (MHz) of Rotational Transitions of Oxiranecarbonitrile in the Vibrational Ground State
63
TABLE 4 Diagonal 14N Quadrupole Coupling Constants and Correlation Coefficients of Oxiranecarbonitrile in the Vibrational Ground State a
nuclear quadrupole coupling constants of oxiranecarbonitrile were estimated when the quadrupole coupling tensor of cyclopropyl cyanide (19) was transformed to the principal axes of oxiranecarbonitrile. The assignments of the hyperfine splittings of rotational transitions followed directly from this estimate. The measured frequencies of the quadrupole components are listed in Table 3. The small splittings allowed the fitting of only two diagonal quadrupole coupling constants of the traceless tensor. The measured splittings were not TABLE 5 Stark Slopes (Hz V 02 cm2 ) and Electric Dipole Moment (D) of Oxiranecarbonitrile a
at least one R-branch transition. A few R-branch transitions were assigned from microwave–microwave double-resonance experiments (17). A suitable transition of the assigned Q-branch was pumped while searching for an R-branch transition which had a common energy level with the Q-branch transition. The accurately measured frequencies of the finally assigned transitions are listed in Table 1. Three rotational constants and five quartic centrifugal distortion constants were fitted simultaneously to the measured transition frequencies. The centrifugal distortion constants are defined according to Watson’s asymmetric reduction in the prolate I r-representation (18). The results of the leastsquares fit are collected in Table 2 with uncertainties given in parentheses as one standard deviation. (b) Quadrupole Coupling Constants In order to determine the quadrupole coupling constants due to the 14N nucleus accurately, some low J transitions were measured with the FTMW spectrometer. Preliminary Copyright q 1996 by Academic Press, Inc.
AID
JMS 7053
/
6t0d$$$201
07-09-96 13:25:55
mspal
AP: Mol Spec
64
¨ LLER AND BAUDER MU
TABLE 6 Main Quadrupole Coupling Constant xzz (MHz) in the Bond Direction for Different Nitriles
quadrupole coupling constants were transformed to the bond axis system of the CN group. The transformation was based on an assumed structure with parameters transferred from ethylene oxide (14) and acetonitrile (15). The result for the main quadrupole coupling constant xzz along the CN bond direction is compared in Table 6 to values found in related compounds. The slightly larger value outside the range of the other compounds is not significant in view of the assumed molecular structure. Finally all three components of the permanent electric dipole moment were obtained in the principal axis system from quantitative Stark effect measurements. ACKNOWLEDGMENTS Financial support by the Schweizerischer Nationalfonds (Project 20.33367.92) is gratefully acknowledged. We thank Professor A. Eschenmoser, Professor W. M. Irvine, and Professor G. Arrhenius for stimulating discussions and their interest in the present work. We are indepted to Dr. S. Pitsch for the preparation of a sample of oxiranecarbonitrile.
dependent on the nondiagonal elements. The rotational and the five centrifugal distortion constants were kept fixed at the values of Table 2 during the least-squares fit of the quadrupole coupling constants. The results are given in Table 4 together with the standard deviations in parentheses. (c) Dipole Moment Rotational transitions which showed no resolvable quadrupole splittings were selected for the determination of the electric dipole moment. The Stark effects of four rotational transitions were observed at seven to nine different dc voltages with the FTMW spectrometer equipped with a Stark cell. A regression analysis of the frequency shifts as a function of the applied static electric field verified that each individual M component had a purely quadratic Stark effect. The slopes of the M components determined the dipole moment in a weighted least-squares fit. The necessary Stark coefficients were calculated with second-order pertubation theory (20). The measured slopes are compared to the calculated slopes in Table 5 where the results of the ma , mb , and mc components of the electric dipole moment are collected from the least-squares fit. IV. CONCLUSIONS
The microwave spectrum of oxiranecarbonitrile was observed and 121 rotational transitions were assigned for the ground vibrational state. No transitions in excited vibrational states were identified. This fact demonstrates the rigid framework of the three-membered ring with no low-frequency normal vibrations. Accurate rotational and centrifugal distortion constants were fitted to the measured transition frequencies. The intensities of the rotational transitions should be sufficient for the observation of 13C and 15N isotopomers in natural abundance with modern Fourier transform microwave spectrometers. 14N nuclear hyperfine splittings were resolved for a few transitions from which the diagonal quadrupole coupling constants were determined. The obtained
REFERENCES 1. C. W. Gillies, J. Mol. Spectrosc. 71, 85–100 (1978). 2. J. W. Agopovich, J. Alexander, C. W. Gillies, and T. T. Raw, J. Am. Chem. Soc. 106, 2250–2254 (1984). 3. G. La Brecque, C. W. Gillies, and T. T. Raw, J. Am. Chem. Soc. 106, 6171–6175 (1984). 4. T. T. Raw and C. G. Gillies, J. Mol. Spectrosc. 128, 195–205 (1988). 5. A. Eschenmoser and E. Loewenthal, Chem. Soc. Rev. 21, 1–16 (1992). 6. S. Pitsch, E. Pombo-Villar, and A. Eschenmoser, Helv. Chim. Acta 77, 2251–2285 (1994). 7. S. Pitsch, Ph.D. thesis, Eidgeno¨ssische Technische Hochschule, Zu¨rich, Switzerland, 1993. 8. J. E. Dickens, W. M. Irvine, M. Ohishi, F. Mu¨ller, A. Bauder, G. Arrhenius, and A. Eschenmoser, Origins of Life and Evolution of the Biosphere, in press. 9. J. Ekkers and W. H. Flygare, Rev. Sci. Instrum. 47, 448–454 (1976). 10. A. Bauder, in ‘‘Vibrational Spectra and Structure’’ (J. R. Durig, Ed.), Vol. 20, pp. 157–188, Elsevier, New York/Amsterdam, 1993. 11. B. Vogelsanger and A. Bauder, J. Chem. Phys. 87, 4465–4470 (1987). 12. B. Vogelsanger and A. Bauder, J. Mol. Spectrosc. 130, 249–257 (1988). 13. J. M. L. J. Reinartz and A. Dymanus, Chem. Phys. Lett. 24, 346–351 (1974). 14. C. Hirose, Bull. Chem. Soc. Jpn. 47, 1311–1318 (1974). 15. K. Karakida, T. Fukuyama, and K. Kuchitsu, Bull. Chem. Soc. Jpn. 47, 299–304 (1974). 16. W. Gordy and R. L. Cook, ‘‘Microwave Molecular Spectra,’’ Chap. VII, pp. 271–272, Wiley, New York, 1984. 17. J. Ekkers, A. Bauder, and Hs. H. Gu¨nthard, J. Phys. E: Sci. Instrum. 8, 819–822 (1975). 18. J. K. G. Watson, in ‘‘Vibrational Spectra and Structure’’ (J. R. Durig, Ed.), Vol. 6, pp. 1–89, Elsevier, New York/Amsterdam, 1977. 19. O. Bo¨ttcher, N. Heineking, and D. H. Sutter, Z. Naturforsch. A 44, 655–658 (1989). 20. S. Golden and E. B. Wilson, Jr., J. Chem. Phys. 16, 669–685 (1948). 21. R. A. Creswell, G. Winnewisser, and M. C. L. Gerry, J. Mol. Spectrosc. 65, 420–429 (1977). 22. S. G. Kukolich, J. Chem. Phys. 76, 97–101 (1982). 23. E. Fliege and H. Dreizler, Z. Naturforsch. A 41, 1307–1310 (1986). 24. M. Stolze and D. H. Sutter, Z. Naturforsch. A 40, 998–1010 (1985). 25. K. Vormann, U. Andresen, N. Heineking, and H. Dreizler, Z. Naturforsch. A 43, 283–284 (1988).
Copyright q 1996 by Academic Press, Inc.
AID
JMS 7053
/
6t0d$$$201
07-09-96 13:25:55
mspal
AP: Mol Spec