INFRARED-SPECTROSCOPY AND TIME-RESOLVED DYNAMICS OF THE ORTHO-H-2-OH ENTRANCE CHANNEL COMPLEX

The rotationally resolved infrared spectrum of the prereactive o-H-2-O H complex in its ground electronic state is obtained in the OH overton e region at similar to 1.4 mu m using an IR-UV double resonance fluore scence enhancement technique. The pure OH overtone band of o-H-2-OH is observed as well as approximately 20 additional rovibrational transit ions extending out to the OH (X (II)-I-2,v=2) +o-H-2(X (1)Sigma(g)(+)) dissociation limit. These transitions are assigned as combination ban ds involving the simultaneous excitation of the OH vibrational overton e and intermolecular bending (internal rotor) states. The assignment o f the experimental spectrum is aided by a detailed comparison with the bound states computed for the ab initio potential of Clary, Werner, a nd co-workers [Mol. Phys. 83, 405 (1994)]. The infrared spectroscopy r esults also verify the topology of this ab initio potential in the ent rance channel to the OH + H-2 hydrogen abstraction reaction. Direct ti me-resolved experiments indicate that the lifetime of the vibrationall y activated o-H-2-OH complex in the ground intermolecular state is 115 (26) ns. The initial excitation is found to stay localized in the OH i ntramolecular stretching mode for a long period of time prior to vibra tional predissociation or chemical reaction. (C) 1998 American Institu te of Physics.