Rotational and vibrational state distributions of NaH in the reactions of Na(4 2S,3 2D, and 6 2S) with H2:: Insertion versus harpoon-type mechanisms

By using a pump-probe technique, the nascent rotational and vibrational state distributions of NaH are obtained in the Na(4 (2)S,3 (2)D, and 6 (2)S) plus H(2) reactions. The rotational distributions for the Na(4 (2)S,3 (2)D) reactions yield a bimodal feature with a major component peaking at J=20-22, similar to that obtained previously in the 4 (2)P reaction, whereas the Na(6 (2)S) reaction gives rise to a distinct distribution with a much lower rotational temperature. The vibrational populations (v=0-4) for these 4 (2)S, 3 (2)D, and 6 (2)S reactions are characterized by corresponding temperatures of 1692 +/- 120, 819 +/- 35, and 5329 +/- 350 K. Due to a significant contribution of configurational mixing between different states with the same symmetry, the collision species initiated from the 4 (2)S and 3 (2)D states are anticipated to track along the entrance surface in a near C(2v) symmetry, then undergo nonadiabatic transition to the inner limb of the reactive 2A(') surface. In contrast, the reaction pathway for the Na(6 (2)S) state with a significantly reduced ionization energy is anticipated to follow a harpoon-type mechanism via a (near) collinear configuration. The increased atomic size of Na may hinder the insertion approach. (C) 2008 American Institute of Physics.