Vibrational predissociation rate from dynamics of a full collision: A test of the Landau method against the exact results

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Abstract
We applied the Landau method of calculating the coupling matrix element for a bound–free transition to the evaluation of the vibrational predissociation rate constant of the van der Waals complex ICl*–Ne. Use of the adiabatic separation of the radial and angular motion of the van der Waals modes complemented with the angular averaging with the help of the dominant natural expansion wave function of the bending mode, calculated by Lipkin, Moiseyev, and Leforestier [J. Chem. Phys. 98, 1888 (1993)], yields the rate constant which is about 10%–15% lower compared to the best theoretical estimates. This disagreement is ascribed to the true dynamical interaction between the stretching and bending modes which cannot be incorporated into the adiabatic separation of motion of these modes. Different approximations for treating bending motion are discussed and the sensitivity of the rate constant to the variation of principle parameters of the potential energy surface is studied.