Spectroscopy of jet-cooled methane in the lower icosad region: Empirical assignments of low-J″ spectral lines from two-temperature analysis

Abstract

Complete 12CH4 spectrum in the lower icosad spectral range (7050–7350cm−1) has been measured in supersonic jet at 28K for the first time using direct absorption tunable diode laser spectrometer. Due to efficient rotational cooling only spectral lines with lower rotational quantum number J<4 are observed in the spectrum. Spectral lines in the supersonic jet spectra have been matched with those in liquid nitrogen cooled cell spectra (81K) and two-temperature method for empirical lower state rotational quantum number assignments has been applied to obtain accurate experimental values of the lower state rotational quantum numbers J″. Especially positions of lines with of J″=0 are relevant for vibrational band origin determination, as they are unambiguously the R(0) transitions of the respective bands.