Two-photon photodissociation of H2O via the B̃ state

The H2O B̃←X̃ 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 B̃/X̃ conical intersection results in the efficient transfer of flux from B̃ to X̃, with dissociation occurring mainly on X̃ . Though the OH(X2Π) product is highly rotationally excited, this bias is less than that observed at higher energies. The OH(A2Σ+)/OH(X2Π) 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.