Spin-orbit ab initio investigation of the ultraviolet photolysis of diiodomethane

The UV photodissociation (< 5 eV) of diiodomethane (CH2I 2) is investigated by spin-orbit ab initio calculations. The experimentally observed photodissociation channels in the gas and condensed phases are clearly assigned by multi-state second-order multiconfigurational perturbation theory in conjunction with spin-orbit interaction through complete active space-state interaction potential energy curves. The calculated results indicate that the fast dissociations of the first two singlet states of CH 2I2 and CH2I-I lead to geminate-radical products, CH2l• + I(2P3/2) or CH2I• + I*(2P1/2), The recombination process from CH2I-I to CH2I2 is explained by an isomerization process and a secondary photodissociation reaction of CH2I-I. Finally, the study reveals that spin-orbits effects are significant in the quantitative analysis of the electronic spectrum of the CH2I-I species. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.