title: Renner-Teller vibronic analysis for a tetra-atomic molecule. I. The effective Hamiltonian and matrix elements.
abstract: The effective vibronic Hamiltonian for a linear tetra-atomic molecule in a Pi state has been investigated. In addition to the usual vibrational and Renner-Teller coupling terms, the bending mode anharmonicity, spin-orbit coupling, and Fermi resonance interactions have been added to the model. Terms in the Hamiltonian up to the fourth order are given explicitly for molecules of C(infinityupsilon) symmetry and simplifications for symmetric D(infinityh) molecules are discussed. The matrix elements for the HCCS free radical have been obtained and are used to analyze the observed ground-state levels of HCCS and DCCS in a companion paper. The Sears resonance vibronic interaction that couples levels with the selection rules DeltaK=+/-1, DeltaSigma=-/+1, and DeltaP=0 has also been studied and the matrix elements derived. The determinable combinations of signs for the major parameters in the model are discussed.
authors.affiliation: Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055, USA.
authors.forename: Sheng-Gui
authors.initials: SG
authors.lastname: He
authors.forename: Dennis J
authors.initials: DJ
authors.lastname: Clouthier