Infrared spectroscopy and time-resolved dynamics of the ortho-H2–OH entrance channel complex

Abstract

The rotationally resolved infrared spectrum of the prereactive o-H2–OH complex in its ground electronic state is obtained in the OH overtone region at ∼1.4 μm using an IR-UV double resonance fluorescence enhancement technique. The pure OH overtone band of o-H2–OH is observed as well as approximately 20 additional rovibrational transitions extending out to the OH (X 2Π,v=2)+o-H2(X 1Σg+) dissociation limit. These transitions are assigned as combination bands involving the simultaneous excitation of the OH vibrational overtone and intermolecular bending (internal rotor) states. The assignment of the experimental spectrum is aided by a detailed comparison with the bound states computed for the ab initio potential of Clary, Werner, and co-workers [Mol. Phys. 83, 405 (1994)]. The infrared spectroscopy results also verify the topology of this ab initio potential in the entrance channel to the OH+H2 hydrogen abstraction reaction. Direct time-resolved experiments indicate that the lifetime of the vibrationally activated o-H2–OH complex in the ground intermolecular state is 115(26) ns. The initial excitation is found to stay localized in the OH intramolecular stretching mode for a long period of time prior to vibrational predissociation or chemical reaction.