The quenching of Na(3 2P) by H2: Interactions and dynamics

An eight-configuration diatomics-in-molecules formalism with symmetrically orthogonalized diabatic input is used to calculate the three lowest potential energy surfaces and nonadiabatic couplings for Na+H2 collisions. The singlet diatomic input for NaH and the singlet and triplet diatomic input for H−2 are chosen to reproduce the accurate adiabatic curves for those cases, and the diatomic input for H2 is based on theoretical interpretations of the resonance states. Trajectory calculations are carried out using the calculated 2 2A′ potential surface and nonadiabatic couplings, and the choice of H−2 input is found to sensitively affect the H2 vibrational excitation in the resonance-line quenching process. One H−2 curve, based on the work of Wadehra and Bardsley, yields an amount of vibrational excitation similar to that observed experimentally. The resulting set of potential energy surfaces provides a reasonable microscopic interpretation of the chemical dynamics of the quenching process Na(3p2P)+H2(v = 0, low j) →Na(3s2S)+H2(v′,j′).