PRELIMINARY RESULTS ON THE ANALYSIS OF THE PENTAD OF $^{13}CH_{4}$

Abstract

Preliminary results on the simultaneous analysis of infrared and Raman data of $^{13}CH_{4}$ in the $3-\mu m$ region $(\nu_{1},\nu_{3},2\nu_{2},\nu_{2}+\nu_{4},2\nu_{4})$ will be presented. The infrared spectrum of $^{13}CH_{4}$ (90% enriched) has been recorded with the Fourier Transform Spectrometer at Kitt Peak National Observatory. Line positions have been mesured with a relative accuracy of $0.0001 cm^{-1}$ (for well isolated lines) using $0.0118 cm^{-3}$ 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 $v_{1}(A_{1})$ and $2v_{2}(A_{2})$ Q-branches have been recorded in Dijon by inverse Raman Spectroscopy with an instrumental resolution of $0.0022 cm^{-1}$. They were recorded at room temperature and at pressures of 3 torr for $v_{1}$ and 36 torr for $2\nu_{2}$. 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 tonsorial Hamitonian taking lato account all interactions within the pentad up to the fourth-order of approximation (206 parameters). The preliminary analysis has been carried Out throughout $J=13$ involving 1200 data reproduced wich is standard deviation of $0.0007 cm^{-1}$, approximately 30 times better than the most rsecent results published on the $^{12}CH_{4}$ pentad.