Exploring molecular complexity:: Conical intersections and NH3 photodissociation

The role of conical intersections in the photodissociation of the (A) over tilde (1)A(2) state of NH3 is investigated using extended atomic basis sets and a configuration state function expansion of approximately 8.5 million terms. A previously unknown portion of the 1 (1)A-2 (1)A seam of conical intersections with only C-s symmetry is located. This portion of the seam is readily accessible from the equilibrium geometry of the (A) over tilde (1)A(2) state. These conical intersections are expected to play a role in the competition between adiabatic and nonadiabatic pathways for NH3((A) over tilde (1)A(2)) photodissociation. (C) 2004 American Institute of Physics.