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Volume 13: Pages 412-420, 2000

Angular Momentum Coupling Schemes for Molecular Collisions: The Stereodirected Representation

Vincenzo Aquilanti, Simonetta Cavalli, Alessandro Volpi

Dipartimento di Chimica, Università di Perugia, I‐06123 Perugia, Italy

Frame transformation theory and the classification of rotational spectra of diatomic molecules according to the five Hund cases provide a guide to the quantum‐mechanical formulation of alternative coupling schemes for the treatment of atomic collisions between species carrying spin and electronic angular momenta. An account of the corresponding diabatic representations of the orthogonal transformations among cases and of extensions needed to deal with molecular encounters is presented. Basic to these developments are the tools of angular momentum algebra, and in particular the limiting relationships known as semiclassical limits. Alternative representations for the quantum‐mechanical scattering matrix are discussed with reference to the description of steric effects in molecular collisions. Implications for reactive scattering theory, an explicit discretization algorithm (hyperquantization), and numerical results are also outlined.

Keywords: angular momentum, molecular collision, coupling schemes, stereodirected representation, hyperquantization, semiclassical limit, Hund's cases, frame transformation

Received: July 7, 2000; Published online: December 15, 2008