Mode-selective decay dynamics of the ortho-H-2-OH complex: experiment and theory

The predissociation dynamics of ortho-H-2-OH in its ground electronic state are studied in time-resolved experiments and quantum mechanical calculatio ns. The experiments use stimulated Raman and infrared overtone pumping to e xcite the nu(H2) = 1 Or nu(OH) = 2 vibrational states of the complex. The a ppearance of the OH X (II)-I-2 products is monitored as a function of time. Vibrational predissociation lifetimes and rotational product distributions are calculated in full dimensionality with a time-dependent wavepacket tec hnique using a potential energy surface derived from high quality ab initio calculations. Both experiment and theory give predissociation lifetimes fo r nu(H2) = 1 that are an order of magnitude shorter than those for nu(OH) = 2, and only a small number of OH rotational product states are found to be populated. The possibility of inducing chemical reaction via initial vibra tional excitation of H-2-OH is discussed.