Analyses and modeling of the 12CH4 spectrum at 80 K between 6539 and 6800 cm-1

Accurate rovibrational analysis of the lower part of the Icosad (CH4)-C-12 spectrum in the 6539-6800 cm(-1) region is reported. The analysis uses the WKLMC experimental line list previously obtained in Grenoble by Cavity Ring Down Spectroscopy and Differential Absorption Spectroscopy at T=80 K. Based on an ab initio potential energy surface, the full Hamiltonian of methane nuclear motion was reduced to an effective Hamiltonian using high-order Contact Transformations method with a subsequent empirical optimization of parameters. About 2445 experimental line positions were fitted with RMS standard deviations of 0.005 cm(-1) and 1644 line intensities were modeled using effective dipole moment with the RMS deviation of 11.5%. Twenty five vibrational energy levels of the lower part of the Icosad were determined. (C) 2015 Elsevier Ltd. All rights reserved.