We have obtained visible overtone spectra with Dopplerhyphen;limited resolution of methane and trideuteromethane in the vicinity of six quanta of Cndash;H stretch. At room temperature, the methane spectrum is unresolved. Upon cooling to 77 K in a specially designed photoacoustic cell, methane shows a complicated but rotationally resolved spectrum. The widths of all features in the spectrum are consistent with Doppler broadened linewidths at 77 K. Efforts to assign this spectrum are in progress. The overtone spectrum of CD3H has been recently studied by other workers at a resolution of 0.5 cmminus;1lsqb;Perry, Moll, Kupperman, and Zewail (preprint)rsqb;. The spectrum in this region consists of two parallel bands, one at 16thinsp;156 cmminus;1and another at 16thinsp;230 cmminus;1. These are assigned as arising from a Fermi resonance between the pure Cndash;H overtone 6ngr;1and a combination with the degenerate Cndash;H bend, 5ngr;1+2ngr;5. A high resolution spectrum taken at 77 K shows nearly completely resolvedKhyphen;subband structure for both bands. The rotational constants of both states cannot be rationalized purely on the basis of the above vibrational assignment, although it is the most reasonable explanation of the observed vibrational spectrum. Our rotational analysis of the bands indicates that both of these states are in Coriolis resonance with another state or states which are not seen in our spectrum.
展开▼
