Theoretical Studies of Spin-Forbidden and Electronically Nonadiabatic Processes

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With this grant in the Theoretical and Computational Program of the Chemistry Division Professor Yarkony will investigate several problems in spin-forbidden and electronically nonadiabatic chemistry. These processes play a major role in determining the rate of a number of industrially important chemical reactions. Professor Yarkony will develop computer algorithms which will include: (1) the capability for determining relativistic wavefunctions using large scale configuration state function expansions based on quasidegenerate perturbation theory within the Breit-Pauli approximation, and (2) the use of analytical gradient methods for locating regions of significant electronic nonadiabaticity, that is, allowed, avoided and actual crossings of potential energy surfaces, and for determining derivative couplings in these regions. He will consider nonadiabatic electronic quenching reactions such as that between Na+HCl which has been the object of recent experimental and theoretical studies. He will focus on the nature of the adiabatic-diabatic state transformations. Other areas to be investigated include: (1) photochemical dissociation processes, (2) a characterization of the global potential energy surfaces and derivative couplings for the He-H2 system, and (3) a study of spin-forbidden dipole-allowed radiative decay processes in the molecules NO+ and O2+, which are candidates for energy storage intermediates in energy transfer in chemical lasers, as well as the molecules SiCl2, SiH2, and SiHCl which play a role in semiconductor fabrication through vapor deposition.