First principles determination of the NH2∕ND2(Ã,X̃) branching ratios for photodissociation of NH3∕ND3 via full-dimensional quantum dynamics based on a new quasi-diabatic representation of coupled ab initio potential energy surfaces.

The A-band photodissociation of ammonia is an archetypical and long studied example of non-adiabatic dynamics in a polyatomic system. Due to a well-known conical intersection seam, electronically excited NH(3) can produce either the ground (X̃(2)B(1)) state or the excited (Ã(2)A(1)) state of the NH(2) fragment. In this work, the non-adiabatic dynamics is investigated using a six-dimensional wave packet method and an improved version of a newly developed diabatic Hamiltonian based on high quality ab initio data. The Ã(2)A(1)/X̃(2)B(1) branching ratios are in excellent agreement with experimental estimates, thus validating the non-adiabatically coupled Hamiltonian.