An experimental study of OH(A 2 Σ + ) + H 2 : Electronic quenching, rotational energy transfer, and collisional depolarization.

Zeeman quantum beat spectroscopy has been used to determine the thermal (300 K) rate constants for electronic quenching, rotational energy transfer, and collisional depolarization of OH(A2 Σ+ ) by H2 . Cross sections for both the collisional disorientation and collisional disalignment of the angular momentum in the OH(A2 Σ+ ) radical are reported. The experimental results for OH(A2 Σ+ ) + H2 are compared to previous work on the OH(A2 Σ+ ) + He and Ar systems. Further comparisons are also made to the OH(A2 Σ+ ) + Kr system, which has been shown to display significant non-adiabatic dynamics. The OH(A2 Σ+ ) + H2 experimental data reveal that collisions that survive the electronic quenching process are highly depolarizing, reflecting the deep potential energy wells that exist on the excited electronic state surface.