Ab initio potential-energy surfaces of O-2(X-3 Sigma(-)(g),a (1)Delta(g),b(1)Sigma(+)(g))+O-2(X-3 Sigma(-)(g),a (1)Delta(g),b (1)Sigma(+)(g)): Mechanism of quenching of O-2(a (1)Delta(g))

摘要

Ab initio computational studies were carried out in order to explore the possible mechanisms of quenching of O-2(a (1)Delta(g)) by O-2(X (3)Sigma(g)(-)): the self-quenching of O-2(a (1)Delta(g)) and other energy-transfer processes involving two O-2 molecules. All eighteen states arising from two O-2 molecules in the X (3)Sigma(g)(-), a (1)Delta(g), and b (1)Sigma(g)(+) states are considered. After scans at the state-averaged complete active space self-consistent field method to identify possible regions of crossing between states belonging to different asymptotes, complete active state second-order perturbation theory high-symmetry optimization and low-symmetry scans established that four different minima on the seams of crossing (MSXs), arising between the a+a manifold and the X+b manifold and responsible for self-quenching: O-2(a (1)Delta(g))+O-2(a (1)Delta(g))-> O-2(X (3)Sigma(g)(-))+O-2(b (1)Sigma(g)(+)), have coplanar C-2h or C-2v symmetries and are only 0.45 eV barrier relative to the a+a asymptote and energetically easily accessible. The rate constant for this process was estimated based on the Landau-Zener formalism. The MSXs for quenching of O-2(a (1)Delta(g)) by the ground state O-2(X (3)Sigma(g)(-)):O-2(a (1)Delta(g))+O-2(X (3)Sigma(g)(-))-> O-2(X (3)Sigma(g)(-))+O-2(X (3)Sigma(g)(-)) require higher energies and the process is not likely to be important. (c) 2005 American Institute of Physics.