Photodissociation of H2O at 121.6 nm:: A state-to-state dynamical picture

Photodissociation dynamics of H2O at 121.6 nm have been studied using the H atom Rydberg tagging time-of-flight technique and by quasiclassical trajectory (QCT) calculations. Product kinetic energy distributions and angular distributions have been measured. From these distributions, rovibronic distributions of the OH radical product as well as the state resolved angular anisotropy parameters were determined. The dissociation energy D-0(0)(H-OH) is determined to be 41151 +/-5 cm(-1). Two clear alternations in the OH(X,v=0) rotational distribution have been observed, with each alternation corresponding to an oscillation in the anisotropy distribution. These oscillations had been attributed to the dynamical interference between the two conical intersection pathways. Further theoretical modeling in this work strongly supports this argument. Very highly vibrationally excited OH(X) products (up to v=9) have also been observed. These are ascribed to interconversion of H-O-H bending (H-H vibration) and O-H vibration in O-H-H geometries. The effect of parent rotational excitation on the OH(A) product state distribution and anisotropy distribution was observed for the first time. Experimental results also show clear evidence for the triple dissociation channel, O(P-3)+2H. Accurate branching ratios of different product channels have been determined. Results of detailed QCT calculations agree well with the experimental results in this work. (C) 2000 American Institute of Physics. [S0021- 9606(00)00746-7].