State-to-state inelastic scattering from vibrationally activated OH - H2 complexes

State-selective infrared excitation of o-H2 - OH via the pure OH overtone transition has been used to induce a half-collision inelastic scattering event between the OH radical and ortho-H2 under restricted initial orientation conditions. The time evolution and final state distribution of the OH products from vibrational predissociation have been evaluated by ultraviolet probe laser-induced fluorescence measurements. The half-collision scattering takes place with ∼3350 cm-1 of energy available to the OH (v=1)+o-H2 products, an energy that exceeds the classical barrier to reaction. The OH (v=1) products are preferentially populated in high rotational levels with a distribution that is consistent with an energy gap law. A significant fraction of the OH fragments are promoted to the excited spin - orbit state in the predissociation process. A strong lambda-doublet propensity is also found, indicating that the OH unpaired pπ orbital is preferentially aligned perpendicular to the rotational plane of the OH products. Finally, the OH rotational and fine structure distributions are compared with those obtained in previous full collision inelastic scattering studies at energies below the threshold for reaction. copyright 1998 American Institute of Physics