Nonadiabatic interactions in unimolecular decay. IV. Transition probability as a function of the Massey parameter

Publisher Website
Google Scholar
Abstract
The nonadiabatic transition probability P between two electronic states is studied in the semiclassical approximation. Extensive use is made of the concept of global function introduced in the diabatic representation by Delos and Thorson (their t (s) function) and by ourselves in the adiabatic representation (the Massey function, T (S)). Consideration of the shapes of these global functions results in a classification of the different models which have been proposed earlier by Landau and Zener, by Rosen and Zener, by Delos and Thorson, by Nikitin, and by Bandrauk. The relationships which exist between all of these models are displayed. For all of them, the transition probability P can be expressed as a simple analytic expression involving two parameters, ξ and ϑo. ξ is the Massey parameter. ϑo measures the initial decoupling, i.e., the component of the adiabatic states on the basis set of the diabatic states at the initial time (corresponding to the initial excitation in a photochemistry experiment). For a given value of ϑo, the different models predict relationships between P and ξ that do not differ greatly, so that a kind of ’’universal function’’ relating P and ξ can be defined. The previous considerations are applied to three specific examples of nonadiabatic coupling encountered in the case of H2, N2+ and CH2+. For each of them, the global functions t (s) and T (S) are calculated ab initio. The relationship between their shape and the nonadiabatic transition probability is discussed.