The vibrational levels of methane obtained from analyses of high-resolution spectra

Methane and its tetrahedral isotopologues are spherical-top molecules whose high-resolution rovibrational spectra can only be analyzed in detail, thanks to sophisticated symmetry-adapted tensorial models. However, the effective Hamiltonian parameters of such models do not give direct access to the positions of the vibrational sublevels. In this paper, we present a calculation of the vibrational level positions for (CH4)-C-12, (CH4)-C-13, (CD4)-C-12 and (CD4)-C-13 performed using the effective Hamiltonian parameters obtained through recent analyses. We also include the results of a re-analysis of the octad system of (CH4)-C-12 performed with a higher order of the development which slightly improves the previous work on this polyad. (C) 2005 Elsevier Ltd. All rights reserved.