Ab initio molecular orbital study of the mechanism of photodissociation of formamide

In the present Letter, the reaction pathways for H2NCHO decomposition in the ground and excited states are traced with the use of the MP2 and CASSCF energy gradient techniques. The intersection point of the S-1 and T-1 surfaces are determined by means of the state-average CASSCF optimization. The n --> pi* excitation leads to the first excited singlet state, where a radical pair of NH2 and CHO is formed. Then a hydrogen atom transfers from the CHO radical to the NH2 radical, producing CO and NH3 in the ground state. This is in good agreement with recent experimental findings. The calculated results also show that H-2 and HNCO can be formed along a two-step T-1 pathway. A recent experimental study on the photochemistry of the H2NCHO suggested that H-2 elimination from H2NCHO takes place on the T-1 surface. (C) 2000 Elsevier Science B.V. All rights reserved.