SEMINUMERICAL CONTACT TRANSFORMATIONS - FROM INTERNAL COORDINATE ROVIBRATIONAL HAMILTONIAN TO EFFECTIVE ROTATIONAL HAMILTONIANS - FRAMEWORKOF THE METHOD

This paper presents a formulation of seminumerical contact transformat ions for rovibrational spectroscopy. Effective rotational Hamiltonians are obtained starting from a rovibrational Hamiltonian with an exact kinetic energy operator in curvilinear internal valence coordinates. L ike the accuracy of the variational methods, the accuracy of this meth od can be increased by using more computational power. Error estimates are also calculated. Main motivations for using seminumerical contact transformations in rovibrational spectroscopy are considered. As an e xample, a calculation is carried out for H2S. No remarkable deviations between the calculated and the observed effective constants were obse rved for the states considered (ground states, nu(2) nu(1), nu(3), 2 n u(2), 2 nu(1) + nu(2), nu(1) + nu(2) + nu(3), nu(2) + 2 nu(3)) New ide as for further research of this subject are suggested. (C) 1995 Americ an Institute of Physics.