Semiempirical molecular dynamics investigation of the excited state lifetime of ethylene

Semiempirical molecular dynamics with surface hopping was employed to investigate the lifetime of excited states of ethylene. Based on previous ab initio multireference configuration interaction results, a complete reparametrization of the AM1 semiempirical parameters was performed. Depending on the initial vertical excitation energy, lifetimes from 105 to 139 fs were found for the V-state decay. Comparison to the pump-probe experiments was performed in order to explain the large differences between the theoretically and experimentally obtained lifetimes. The results show that probe energies of at least 7.4 eV should be employed to ionize the system for geometries close to the conical intersections. (C) 2004 Elsevier B.V. All rights reserved.