PRELIMINARY-ANALYSIS OF THE PENTAD OF (CH-4)-C-13 FROM RAMAN AND INFRARED-SPECTRA

Preliminary results on the simultaneous analysis of infrared and Raman data of 13CH4 in the 3-μm region (ν1, ν3, 2ν2, ν2 + ν4, and 2ν4) are presented. The infrared spectrum of 13CH4 (90% enriched) has been recorded with the Fourier transform spectrometer at Kitt Peak National Observatory. Line positions have been measured with a relative accuracy of 0.0001 cm-1 (for well-isolated lines) using 0.0118-cm-1 resolution spectra. In order to compensate for the lack of infrared information about low J transitions of vibrational bands forbidden in infrared, two spectra of the ν1 (A1) and 2ν2 (A1) Q branches have been recorded in Dijon by inverse Raman spectroscopy with an instrumental resolution of 0.0022 cm-1. Line positions have been measured with a precision of 0.001 cm-1 using a profile fitting procedure. Raman and infrared data were combined in a weighted least-squares fit to determine vibration-rotation constants. We used an effective tensorial Hamiltonian taking into account all interactions within the pentad up to the fourth order of approximation. The preliminary analysis has been carried out throughout J = 13 involving 1200 data reproduced with a standard deviation of 0.0007 cm-1, approximately 30 times better than the most recent results published on the 12CH4 pentad. © 1991.