State-to-State Photodissociation Dynamics of H2O in the B-band: Competition between Two Coexisting Nonadiabatic Pathways

The photodissociation of H2O in its B band is a prototype for nonadiabatic reaction dynamics. In addition to dissociation via the adiabatic pathway to the OH((A) over tilde (2)Sigma(+)) + H fragments, it also produces the OH((X) over tilde (2)Pi) + H fragments through two nonadiabatic pathways: the (B) over tilde -> (X) over tilde (transition via two conical intersections and the (B) over tilde -> (A) over tilde transition via a Renner-Teller pair. In this work, the state-to-state dissociation dynamics in all three channels are investigated with a full-dimensional quantum mechanical model using a set of coupled diabatic potential energy surfaces determined at the internally contracted multireference configuration interaction level with the aug-cc-pVQZ basis set. The inclusion of all relevant electronic states not only results in an improved agreement with the latest experimental data but also sheds valuable insights into the competition between the two coexisting nonadiabatic pathways.