Hydrogen-atom photofragment spectroscopy. Photodissociation dynamics of H2O in the B–X absorption band

Abstract

The photofragmentation dynamics of H₂O molecules following vacuum ultraviolet laser excitation at wavelengths within the B¹A₁–X¹A₁ absorption band have been investigated using a novel from of photofragment translational spectroscopy. Analysis of the nascent H atom time-of-flight spectra confirms the importance of the dissociation channel leading to ground-state H + OH products. In addition, it reveals that the OH(X) fragments are formed predominantly in their zero-point vibrational level with a highly excited, inverted rotational-state population distribution. A consideration of the topology of the various potential-energy surfaces sampled by the H₂O molecules during this electronically non-adiabatic dissociation process suggests a likely explanation for this observed pattern of energy disposal.