Reaction dynamics ofNa*(42P)+H2: Effect of reactant orbital alignment on reactivity and product rotational state distribution

We have investigated the direct reaction of ${\mathrm{Na}}^{\mathrm{*}}$(4 ${}_{}{}^2{}_{}{}^{}$P) with ${\mathrm{H}}_2$ to form the product NaH. Using far-wing absorption techniques, we have measured absorption into the ${\mathrm{NaH}}_2$ collision complex, followed by branching into nonreactive (formation of ${\mathrm{Na}}^{\mathrm{*}}$) or reactive (formation of NaH[X ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$(v’ ’,J’ ’)]) 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 v’ ’=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.