Full-Dimensional Quantum Dynamics of Vibrationally Mediated Photodissociation of NH3 and ND3 on Coupled Ab Initio Potential Energy Surfaces: Absorption Spectra and NH2((A)over-tilde2A1)/NH2((X)over-tilde2B1) Branching Ratios

Vibrationally mediated photodissociation of NH3 and ND3 in the A band allows the exploration of the excited-state potential energy surface in regions that are not accessible from the ground vibrational state of these polyatomic systems. Using our recently developed coupled ab initio potential energy surfaces in a quasi-diabatic representation, we report here a full-dimensional quantum characterization of the (A) over tilde <- (X) over tilde absorption spectra for vibrationally excited NH3 and ND3 and the corresponding non-adiabatic dissociation dynamics into the NH2((A) over tilde (2)A(1)) + H and NH2((X) over tilde B-2(1)) + H channels. The predissociative resonances in the absorption spectra have been assigned with appropriate quantum numbers. The NH2((A) over tilde (2)A(1))/NH2((X) over tilde B-2(1)) branching ratio was found to be mildly sensitive to the initial vibrational excitation prior to photolysis. Implications for interpreting experimental data are discussed.