6533b86efe1ef96bd12cb254

RESEARCH PRODUCT

Preliminary analysis of the pentad of 13CH4 from Raman and infrared spectra

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Abstract Preliminary results on the simultaneous analysis of infrared and Raman data of 13 CH 4 in the 3-μm region ( ν 1 , ν 3 , 2 ν 2 , ν 2 + ν 4 , and 2 ν 4 ) are 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 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 ν 1 ( A 1 ) and 2 ν 2 ( A 1 ) 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 12 CH 4 pentad.