On the physical interpretation of torsion–rotational parameters for CH3OD isotopomers Original Research Article

Using the formulation (Phys. Lett. A 207 (1995) 203) of the centrifugal distortion effects in terms of the potential parameters for a molecule that contains a threefold symmetric internal rotor, molecular parameters have been determined for the 12C and 13C isotopomers of CH3OD with O-16, 17 and 18. The calculated parameters, especially the constants that represent interactions between torsion and rotation, are used to interpret the relationships among the terms in the reduced Hamiltonian and in the analysis of the observed torsion–rotational spectrum. Molecular parameters are calculated from several potential energy functions for methanol isotopomers to check the quality of these potentials. The dependence of torsion–rotational parameters on the mass of atom and the geometric parameters are addressed by comparisons of calculated values for various isotopomers of CH3OD. The parameters are compared with the parameters that were obtained from several global fits to experimental spectrum data. The good agreement between the calculated torsion–rotational parameters and those derived from the global fits demonstrates that the derived formulae provide a useful tool for understanding the physical origins of the Hamiltonian parameters and the dependence of torsion–rotational parameters on fundamental molecular parameters.