Ab initio calculations of potential energy surface and rate constants for ethylene photodissociation at 193 and 157 nm

The transition states and intermediates of the atomic and two molecular hydrogen elimination channels on the ground state potential energy surface of C2H4 have been characterized at the B3LYP/6-311G(d,p) level of calculations. The corresponding energies have been computed by the CCSD(T)/6-3ll + G(3df, 2p) method. Ethylidene was found to be a likely intermediate in 1,2 H-2 elimination channel. Rate constants of C2H4 photodissociation at 193 and 157 nm have been obtained according to the RRKM theory, based on the results from the ab initio calculations. The study indicates that the hydrogen atom loss channel is favored at higher excitation energy, which is consistent with the experimental observations. (C) 1998 Elsevier Science B.V. All rights reserved.