Dissociation of NH3 to NH + H2
The dissociation paths NH3→ NH + H2 have been investigated for the X1A′1, Ã1A″2 and ã3A″2 electronic states of ammonia. Depending on the point group used to describe the dissociation, the NH3 electronic states correlate with different asymptotes: the electronic ground state with the a 1Δ(NH)+1Σ+g(H2) and X 3Σ–(NH)+3Σ+u(H + H); the Ã1A″2 state with a 1Δ, b 1Σ+, c 1Π(NH)+1Σ+g(H2) and X 3Σ–(NH)+3Σ+u(H + H); the ã3A″2 with X 3Σ–(NH) and A 3Π(NH)+1Σ+g(H2), respectively. Parts of these dissociative paths of the potential-energy functions have been mapped using CASSCF ab initio wavefunctions. In the C2v structures the X 1A′1 state possesses a high barrier reaching into the energy region of the Ã1A″2 and B 1E″ states. No such barriers exist for the Ã1A″2 and ã1A″2 states. The X 1A′1, Ã1A″2 and the B 1E″ states as well as the ã3A″2 and b 3E″ states of ammonia possess common conical intersections, leading to vibronic coupling effects among those states. The Ã1A″2 dissociates mainly into NH2(X 2B1)+ H, the ã3A″2 state into NH(X 3Σ–)+ H2(X 1Σ+g) products.