Dissociation dynamics of the water molecule on the (A)over-tilde B-1(1) electronic surface

Photodissociation of H2O, D2O, and HOD on the (A) over tilde B-1(1)' surfac e through 157.6 nm excitation has been studied using the H(D) atom Rydberg tagging time-of-flight technique. Vibrational state distribution has been m easured for the OH/OD product from the photodissociation of the H2O, D2O, a nd HOD molecules. Comparisons of our results with previous theoretical calc ulations and experimental results obtained using the laser induced fluoresc ence (LIF) technique have been made. Experimental results in this work indi cate that the relative populations for vibrationally excited OH(v greater t han or equal to2) products measured using LIF are significantly underestima ted, suggesting that LIF as a technique to quantitatively measure vibration al distributions of reaction product OH is seriously flawed. The experiment al results presented here are in rather good agreement with previous theore tical calculations. However, our results indicate that the calculated vibra tional populations for the higher vibrational states of OH are still somewh at overestimated. Relative branching ratio of H and D productions from HOD has also been estimated. This complete set of data for the photodissociatio n of H2O should provide an excellent testing ground for improving the theor etical potential energy surface of the first electronically excited state o f the water molecule. (C) 2000 American Institute of Physics. [S0021-9606(0 0)01220-4].