Dissociation of NH3 to NH2+H

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

Potential energy, dipole moment, and electronic transition moment surfaces for the lowest dissociative pathways of the singlet X˜ and A˜ states of NH3 yielding NH2 (X˜ 2B1,A˜ 2A1) +H(2S) products have been calculated using complete active space MCSCF ab initio wave functions. The A˜ state dissociation proceeds via a minimum barrier at the following planar geometry: αHNH =113°, rNH =1.042 A(ring) (in the NH2 fragment), and RNH =1.323 A(ring) (in the dissociation coordinate). The barrier height is calculated to be 3226 cm−1 with an expected accuracy of about 300 cm−1. The barrier height increases with increasing out-of-plane angle. Close to the barrier there are strong variations of the shapes of the dipole moment and transition moment surfaces. The minimum energy path through the X˜–A˜ conical intersection follows planar geometries. Along this pathway the angle αHNH decreases, but the distance rNH in the NH2 fragment hardly changes. The crossing distance RcNH of the X˜ and A˜ states in planar structures depends strongly on αHNH and varies from about 1.68 A(ring) (60°) to infinity (180°). The photodissociation process NH3(A˜) →NH2(X˜ 2B1) +H(2S) is discussed on the basis of the calculated potential energy surfaces.

Electronic Resource