Ab initio molecular orbital and dynamics study of transition-state spectroscopy

Recent results on the ab initio potential-energy surface (PES) and dynamics calculations closely related to the experiments of ‘transition-state spectroscopy’(TSS) are discussed. The topics included are the photodissociations of NaI and ozone, and the unimolecular dissociation of FHF–. The non-adiabatic coupling in the ion–covalent crossing region of the NaI dissociation is calculated based on the CASSCF-MRCI method and compared with experimental and empirical estimates. The PESs of the ozone photodissociation are calculated using the CASSCF-SECI method. Characteristics of the ground and the excited B-state PESs are compared with the existing PESs. The weak structure seen in the Hartley band is explained in terms of transition-state dynamics based on three-dimensional quantum calculations using new PESs. The CEPA PES of the unimolecular dissociation of FHF– to the F–+ HF channel is calculated. Based on the quantum-mechanical variational calculation, the vibrationally highly excited FHF– anion above its dissociation threshold is suggested as a candidate of TSS of unimolecular dissociation reactions without a barrier.