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Published February 1, 1985 | Published
Journal Article Open

High-energy overtone spectroscopy of some deuterated methanes


High-energy overtone photoacoustic spectroscopy of gas phase CHD3 (ΔνCH=5,6, and 7), CH2D2, CH3D, and CH4 (ΔνCH=6) is reported. The overtone and combination bands of CHD3 display partially resolved rotational structure with laser limited linewidths (~0.5 cm^−1). A combination sum analysis is used to generate excited state rotational constants B'. We present an analysis of the Fermi resonances of CHD3 which indicates strong interactions of the CH stretch with degenerate bending modes. The relative intensities of the Fermi interacting states are in agreement with those calculated from an analysis based on frequency shifts and a two or three level model. However, the rotational B' constants are not explained by such simple models indicating further interactions with states as yet unobserved. An upper limit of 10 cm^−1 is estimated for the splitting of the |6,0>± local mode states for CH2D2, giving support to a description based on the local mode picture. For CH3D and CH4 the spectra are apparently congested by overlapping overtone and combination bands and perhaps other mechanisms not identified in this work. Generally, our results emphasize the importance of the interactions of CH stretching with CH bending motions.

Additional Information

© 1985 American Institute of Physics. Received 7 November 1983; accepted 15 October 1984. AHZ would like to thank Professor R. Zare and Dr. D. Chandler for communicating unpublished results on gas phase halomethanes during a visit to Stanford University. We gratefully thank Professor K. Janda and Professor R. Marcus for discussions, Dr. J.J. Barret for the help with the design of the photoacoustic cell and Professor J. Beauchamp for providing us with some samples used in these studies. We would also like to thank Dr. K. Lehmann and Dr. A. Pine for comments and suggestions. This work was supported in part by grants from the National Science Foundation (Grant No. CHE-8211356) and the U.S. Department of Energy (Contract No. DE-AS03-76SF0067). [A.H.Z. was a] Camille and Henry Dreyfus Foundation Teacher-Scholar. Arthur Amos Noyes Laboratory of Chemical Physics, Contribution No. 6935.

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