Two-photon photodissociation of H2O via the B state

The H2O (B) over tilde <-- (X) over tilde system has been excited by using 266 nm two-photon absorption, and H-atom products have been probed by using high-n Rydberg time-of-flight spectroscopy. The (B) over tilde/(X) over tilde conical intersection results in the efficient transfer of flux from (B) over tilde to (X) over tilde, with dissociation occurring mainly on (X) over tilde. Though the OH (X(2)Pi) product is highly rotationally excited, this bias is less than that observed at higher energies. The OH(A(2)Sigma(+))/OH(X(2)Pi) branching. ratio is <0.1%, which is significantly smaller than branching ratios obtained at higher excitation energies, and two orders of magnitude less than predicted by theory. (C) 2004 Published by Elsevier B.V.