New assignments in the 2 μm transparency window of the 12CH4 Octad band system

This paper reports new assignments of rovibrational transitions of (CH4)-C-12 bands in the range 4600-4887 cm(-1) which is usually referred to as a part of the 2 mu m methane transparency window. Several experimental data sources for methane line positions and intensities were combined for this analysis. Three long path Fourier transform spectra newly recorded in Reims with 1603 m absorption path length and pressures of 1,7 and 34 hPa for samples of natural abundance CH4 provided new measurements of (CH4)-C-12 lines. Older spectra for (CH4)-C-13 (90% purity) from JPL with 73 m absorption path length were used to identify the corresponding lines. Most of the lines in this region belong to the Octad system of (CH4)-C-12. The new spectra allowed us to assign 1014 new line positions and to measure 1095 line intensities in the cold bands of the Octad. These new line positions and intensities were added to the global fit of Hamiltonian and dipole moment parameters of the Ground State, Dyad, Pentad and Octad systems. This leads to a noticeable improvement of the theoretical description in this methane transparency window and a better global prediction of the methane spectrum. (C) 2012 Elsevier Ltd. All rights reserved.