State-to-state inelastic scattering from vibrationally activated OH-H-2 complexes

State-selective infrared excitation of o-H-2-OH via the pure OH overtone tr ansition has been used to induce a half-collision inelastic scattering even t between the OH radical and ortho-H-2 under restricted initial orientation conditions. The time evolution and final state distribution of the OH prod ucts from vibrational predissociation have been evaluated by ultraviolet pr obe laser-induced fluorescence measurements. The half-collision scattering takes place with similar to 3350 cm(-1) of energy available to the OH (v =1 )+ o-H-2 products, an energy that exceeds the classical barrier to reaction . The OH (v=1) products are preferentially populated in high rotational lev els with a distribution that is consistent with an energy gap law. A signif icant fraction of the OH fragments are promoted to the excited spin-orbit s tate in the predissociation process. A strong lambda-doubler propensity is also found, indicating that the OH unpaired p pi 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 energie s below the threshold for reaction. (C) 1998 American Institute of Physics. [S0021-9606(98)01248-3].