Reactive collision dynamics of Na(42P)+H2 and HD : experiment and theory

We have used a ‘‘half-collision’’ pump–probe technique to measure the far wing absorption profiles of the NaH2 collision complex leading to the nonreactive formation of Na* and to four distinct final rotational states of the reaction product NaH(v″=1, J″=3, 4, 11, and 13). We have observed reaction on both the attractive potential energy surfaces and over a barrier on the repulsive surface. We have observed the effect of the Na* reagent electronic orbital alignment on the NaH final product rotational state distribution. Specifically, absorption to the repulsive surface leads preferentially to low-rotational product states, while absorption to the attractive surfaces leads preferentially to high-rotational product states of NaH. Isotopic substitution experiments give evidence of a kinematic isotope effect on the product rotational state distribution for reactive trajectories on the repulsive surface. We have developed a simple model using a quantum mechanical line shape calculation to estimate the NaH2 absorption probability as a function of wavelength. We then make simple phenomenological dynamical arguments to predict final state branching. There is an overall qualitative agreement between the experimental results and theoretical model predictions.