Choice of the reduction and of the representation in centrifugal distortion analysis: A case study of dimethylsulfoxide

The millimeter-wave and submillimeter-wave spectra of dimethylsulfoxide have been measured up to 660 GHz, corresponding to maximum values of J = 70 and Kc = 68. A total of 3331 transitions (corresponding to 2133 distinct frequencies) were fit to a standard Watson Hamiltonian using the S- and A-reductions and the representations Ir and IIIr. Although dimethylsulfoxide is an asymmetric oblate top, the combination (A, IIIr) gives the worst results. From the point of view of the convergence of the Hamiltonian, the best results are obtained with the combination (S, IIIr) but the least-squares system of normal equations is better conditioned with representation Ir. These results are compared to those obtained for a few typical molecules.