Orientation and alignment depolarization in OH(X Π2)+Ar/He collisions

The depolarization of OH(X Π23/2,v=0,J=1.5–6.5,e) rotational angular momentum (RAM) in collisions with He and Ar under thermal conditions (298 K) has been studied using two-color polarization spectroscopy (PS). Orientation or alignment of the OH RAM was achieved using circularly or linearly polarized pulsed excitation, respectively, on the off-diagonal OH A Σ2+−X Π2(1,0) band. The evolution of the ground-state OH(X) RAM polarization, exclusively, was probed using an independent, linearly polarized pulse tuned to the diagonal OH A Σ2+−X Π2(0,0) band. The PS signal decay rate constant kPS decreases with increasing rotational quantum number for OH(X)+Ar but does not vary monotonically for OH(X)+He. The measured kPS equals the sum kRET+kΛ+kdep, where kRET, kΛ, and kdep are the rate constants for rotational energy transfer, Λ-doublet changing collisions, and rotationally elastic depolarization (of orientation or alignment of the OH(X) angular momentum, as specified), respectively. Values of kdep can be extract...