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Theory of vibrational predissociation of van der Waals complex in the adiabatic approximation model

1986; American Institute of Physics; Volume: 85; Issue: 12 Linguagem: Inglês

10.1063/1.451397

1520-9032

T Kokubo, Y. Fujimura,

Molecular Spectroscopy and Structure

A theory of the vibrational predissociation (VPD) of linear triatomic van der Waals (vdW) complexes in the adiabatic approximation model is developed aiming to evaluate the VPD rates from higher quantum states as well as the lowest one of the initially excited intramolecular vibrational mode. The adiabatic wave functions of the high frequency intramolecular mode and the adiabatic potential curves are constructed from a Morse-type interaction potential between the two neighboring atoms of the vdW bond. Using Fermi’s Golden Rule, expressions for the rate of the VPD are derived both in the Condon approximation and in the non-Condon scheme. Important contribution of the non-Condon scheme in the adiabatic approximation model is demonstrated by performing model calculations of the VPD rate constants of I2X vdW complexes. The magnitudes of the rate constant in the Condon approximation are smaller than those in the non-Condon scheme by about one to two orders. It is shown that there is a good correspondence in the vibrational quantum number dependence between the treatment in the adiabatic approximation model and that in the scattering theory based on the zero-order diabatic basis set derived by Beswick and Jortner, and that the magnitudes of the vibrational predissociation rate constant calculated by them exist between those in the Condon approximation and in the non-Condon scheme. An approximate expression for the potential displacements between two adiabatic potentials and that for the intramolecular frequency shifts are also derived.