Physics
Scientific paper
Jan 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007jqsrt.103..102w&link_type=abstract
Journal of Quantitative Spectroscopy and Radiative Transfer, Volume 103, Issue 1, p. 102-117.
Physics
7
Scientific paper
The perturbation-allowed distortion moment spectrum of CH4 has been studied between 20 and 100cm with a Fourier transform spectrometer at a temperature of 113.5K similar to that in the atmospheres of Saturn and Titan. Data were obtained at a resolution of 0.06cm and of 0.24cm with a sample gas pressure of 794Torr using an absorption path length of 60.0m. For each (J+1←J), the tetrahedral fine structure was blended together into a single R(J) envelope. Six such envelopes for J=3 8 were measured, the strongest having a signal-to-noise ratio ˜80. From an intensity analysis of R(5), R(6), and R(7), the distortion dipole moment μD of methane was determined to be 23.82(0.88) and 23.94(1.20)μD from the low- and high-resolution spectra, respectively, in excellent agreement with earlier less precise intensity measurements at room temperature and the value of 24.06(0.45)μD obtained from the Stark effect by Ozier [Ground-state electric dipole moment of methane. Phys Rev Lett 1971;27: 1329 32]. Based on these results, it is recommended that the intensities for these transitions in the HITRAN/GEISA data bases be scaled upward by a factor of 1.154. This line spectrum arising from centrifugal distortion mixing was superimposed on a broad continuum due to collision-induced translation-rotation transitions. This continuum was measured from 20 180cm (with a gap between 100 and 120cm), and is compared with the theoretical model of Borysow and Frommhold [Collision-induced rototranslational absorption spectra of CH4 CH4 pairs at temperatures from 50 to 300 K. Ap J 1987;318:940 3] at a lower temperature and with higher absolute accuracy than previously possible. Two features near 125.6 and 157.3cm, each ˜5cm wide, are seen to arise from rotational transitions in CH4 CH4 dimers. The study of the distortion dipole spectrum has direct application to the measurement of the CH4:H2 ratio and the temperature structure in the atmospheres of the Giant Planets and Titan.
Gush H. P.
Orton Glenn S.
Ozier Irving
Wishnow Edward H.
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