NON-ADIABATIC INTERACTIONS IN UNIMOLECULAR DECAY .5. CONICAL AND JAHN-TELLER INTERSECTIONS

The purpose of the present paper is to discuss the properties of conical and Jahn-Teller intersections within a unified formalism. A classical trajectory description of the nuclear motion is adopted throughout. A linear transformation introduced by Nikitin defines a new diabatic basis which is specific of each particular straight line trajectory; this reduces a bidimensional surface intersection problem to an equivalent one-dimensional curve-crossing problem. For each representation (diabatic or adiabatic), it is possible and advantageous to express the transition probability in terms of a single function of a single variable (which we call the global function) instead of the four functions in terms of which the problem is originally defined (i.e., the two energies, the coupling matrix element, and the nuclear velocity). The use of such global functions provides the most general way to express the nonadiabatic transition probability in terms of quantities directly connected with ab initio calculations. Illustrative calculations are presented for the H2CO+ ion, whose dissociation mechanisms are controlled by a conical intersection. © 1979 American Institute of Physics.