Quenching of Li (2P) by H2:: potential energy surfaces, conical intersection seam, and diabatic bases

The quenching of Li (1s(2)2p;P-2) to Li (1s(2)2s;S-2) by H-2 is considered using coupled-cluster and multireference configuration-interaction techniques. C-2 upsilon((2)A(1), B-2(2)) and C-infinity upsilon((2)Pi,( 2)Sigma(+)) sections of the 1(2)A' and 2(2)A' potential energy surfaces are determined. The C-2 upsilon, portion of the 1(2)A' - 2(2)A' seam of conical intersection is studied. Perhaps the most significant finding is a surprising trifurcation of this seam into a portion with only C-s symmetry and the aforementioned C-2 upsilon portion. The adiabatic-to-diabatic state transformation is considered in the vicinity of the seam of conical intersection using both perturbation theory and the dipole moment operator. The B-2(2) section of the 2(2)A' potential energy surface exhibits an exciplex in the general vicinity of the seam of conical intersection. The (2)Pi section of the 2(2)A' potential energy surface possesses a global minimum lying 1.86 kcal/mol below the Li (P-2) + H-2 asymptote. A van der Waals-like minimum with C-infinity upsilon symmetry was Found on the 1(2)A' potential energy surface.