Classical models for electronic degrees of freedom: Derivation via spin analogy and application to F*+H2→F+H2

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Abstract
By invoking the formal equivalence of a finite level quantum mechanical system to a quantum spin in an external field, this paper shows how a classical model can be constructed for an arbitrary finite level quantum system. For two-state and three-state cases this leads to the same classical Hamiltonian that was obtained earlier by other more heuristic methods, but it shows how to treat the general F-state case. The purpose of this overall approach is to be able to represent the electronic states in electronically nonadiabatic collision processes by a classical degree of freedom so that all degrees of freedom, electronic and heavy particle (i.e., translation, rotation, and vibration) can be treated on a consistent dynamical footing. Application of this model to the quenching of F* (2P1/2) by collisions with H2 is described, and this completely classical approach is seen to give excellent agreement with the quantum mechanical coupled channel calculations of Rebentrost and Lester.