Reaction dynamics of Na sup (4 sup 2 P )+H sub 2 : Effect of reactant orbital alignment on reactivity and product rotational state distribution

We have investigated the direct reaction of Na{sup *}(4 {sup 2}{ital P}) with H{sub 2} to form the product NaH. Using far-wing absorption techniques, we have measured absorption into the NaH{sub 2} collision complex, followed by branching into nonreactive (formation of Na{sup *}) or reactive (formation of NaH({ital X} {sup 1}{Sigma}{sup +}({ital v}{prime}{prime},{ital J}{prime}{prime}))) channels. We have observed the reaction to occur both via the attractive potential-energy surfaces and over a barrier on the repulsive surfaces. We have studied the effect of reactant orbital alignment on product rotational distribution for {ital v}{prime}{prime}=1. Specifically we find reaction on the repulsive surfaces leads preferentially to low rotational product states of NaH, while reaction on the attractive surfaces leads preferentially to high rotational states.