Photodissociation of N2O. I. Ab initio potential energy-surfaces for the low-lying electronic states (X)over-tilde (1)A ', 2 (1)A ', and 1 (1)A ''

Adiabatic potential energy surfaces of the three lowest lying singlet state s, (X) over tilde(1)A 2 (1)A', and 1 (1)A ", of N2O have been computed as a function of the RN2-O bond distance and the Jacobi angle. The calculations are performed using the complete active-space self-consistent field (CASSC F) and the multireference configuration interaction (MRCI) electronic struc ture methods. It is shown that there is a wide avoided crossing between the ground, (X) over tilde(1)A', and lowest excited, 2 (1)A', electronic state . This avoided crossing is thought to give rise to a seam of conical inters ection at other N-N separations. Both excited state surfaces display import ant conical intersections at linear geometries. The transition dipole momen t surfaces for the two excitation processes (2 (1)A' <-- (X) over tilde (1) A' and 1 (1)A " <-- (X) over tilde (1)A') are also presented. These calcula tions provide the basic data needed to compute the dynamics of the N2O + hv --> N-2 + O(D-1) photodissociation process for photon frequencies in the r ange 5.2 eV (240 nm) to 7.3 eV (170 nm).