Theoretical Studies of Spin-Forbidden Processes within the Breit-Pauli Approximation

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Abstract : This program considered the electronic structure aspects of radiative and radiationless decay processes related to the stability and formation of high energy density materials. To accomplish this goal a unique system of electronic structure algorithms, the BROOKLYN programs, has been developed. These programs provide advanced capabilities for the study of the electronic structure aspects of spin-forbidden and electronically nonadiabatic processes The methodology is based exclusively on large scale configuration state function expansions (100000 - 1000000 terms). These methods permit significant contributions to the understanding of radiative and radiationless decay processes. Problems of particular relevance to the high energy density materials program include: (i) a study of the possible stability of the energetic maximum ionicity state (HeH)+ to H-; (ii) a study of the spin-forbidden decay mechanism of the model azide system N3H(1A') yields N2(1 Sigma (+) sub g) + NH(X 3Sigma(-)) and finally a study of the decay pathways for the metastable excited state of the helium atom, He(23S), resulting from collisions with other (ground state) helium atoms. Finally a new phase of program development has been initiated focusing on the efficient determination of regions of allowed and avoided crossings of potential energy surfaces using analytic gradient techniques. This program development will provide powerful new tools for the study of spin-forbidden and electronically nonadiabatic processes. (jhd)