Ab initio molecular dynamics study of cis-trans photoisomerization in ethylene

We have used ab initio multi-electronic state molecular dynamics to study t he photoinduced cis-trans isomerization of ethylene. The initial motion on the excited state is a stretching of the C=C bond and the photoisomerizatio n begins within similar to 50 fs of optical excitation. Quenching to the gr ound electronic state is found to be ultrafast and proceeds from an ionic s tate via a conical intersection Accessing the conical intersection requires pyramidalization of one of the methylene groups and this can happen only a fter energy is funneled from the twisting mode into the pyramidalization mo de. (C) 1998 Elsevier Science B.V. All rights reserved.