Vibrationally mediated dissociation dynamics of H2O in the vOH=2 polyad

Vibrationally mediated photodissociation dynamics of jet-cooled H2O in the v(OH)=2 polyad is studied in a supersonic slit jet expansion. Single rotational states within \02>(-) (equivalent tonu(1)+nu(3) in normal mode notation), \02>(+)(equivalent to2nu(1)), \11>(+)(equivalent to2nu(3)), and \01(-)2>(equivalent tonu(3)+2nu(2)) vibrational states of H2O are selectively prepared with near IR overtone pumping, photodissociated at 193 nm, and the resulting nascent internal state distribution of OH fragments probed via laser induced fluorescence. Strong oscillations in rotational, spin-orbit, and lambda-doublet distributions are observed, often in remarkably close agreement with H2O state-to-state photodissociation studies from both higher and lower v(OH) polyads. The influence of initially excited bending and J(K a K c) levels of H2O on spin-orbit, Lambda-doublet, and rotational distributions of OH is examined in detail. Several new dynamical trends are identified, for example, a clear propensity at high N for a strong Lambda(+) versus Lambda(-) inversion in the Pi(3/2) spin-orbit manifold, which reverses in the Pi(1/2) manifold, suggesting spin-orbit sensitive stereodynamics in the ejection process. Furthermore, the results highlight significant differences in photodissociation dynamics from gerade (e.g., \02>(+)) versus ungerade (e.g., \02>(-)) vibrational states, specifically with respect to OH(v=1)/OH(v=0) branching ratios, and signaling a breakdown of the spectator model at low vibrational excitation. (C) 2003 American Institute of Physics.