Collisional redistribution of circularly polarized light in barium perturbed by argon

We have measured the orientation of the Ba 6p ^1P level produced by collision-induced excitation from the ground state by circularly polarized light. The detuning dependence of the far-wing excited-state orientation can be interpreted in terms of reorientation of molecular orbitals which occur during the collision. Effects due to rotational coupling are seen to occur at large blue-wing detunings. We have also determined the collisional rate for destruction of orientation by measuring the pressure dependence of the excited-state orientation.