15min:

O. M. LYULIN, Laboratory of Theoretical Spectroscopy, Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences, 1, Akademicheskii av.,634055 Tomsk; S. KASSI, A. CAMPARGUE, Laboratoire de Spectrométrie Physique (associated with CNRS, UMR 5588), Université Joseph Fourier de Grenoble, B.P. 87, 38402 Saint-Martin-d'Hères Cedex, France; K. SUNG, L. R. BROWN, Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr.,Pasadena, CA 91109, U.S.A..

The high resolution absorption spectra of ¹³CH₄ were recorded at 81 K by differential absorption spectroscopy using a cryogenic cell and a series of Distributed Feed Back (DFB) diode lasers at room temperature by Fourier transform spectroscopy (a Bruker IFS-125HR at JPL). Empirical line lists were constructed containing, respectively, 1629 ¹³CH₄ transitions detected at 81 K (5852~-~6124 cm^-1) and 3481 features measured at room temperature (5850~-~6150 cm^-1); the minimum observed intensities were, respectively, 3×10^-26 and 4×10^-25 cm/molecule at 81 K and 296 K. From the variation of the cold and room temperaure line intensities, empirical lower state energies were derived for 1196 ¹³CH₄ transitions. Over 400 additional weak features, detected at 81 K, could not be matched to lines observed at room temperature. The observed intensities represent 99.2% and 84.6% of the total absorbance at 81 K and 296 K, respectively. The quality of the resulting empirical low energy values is demonstrated by the excellent agreement with the already-assigned transitions and the clear propensity of the empirical low J values to be close to integers.