Ab initio study on the photochemical behavior of styrene

Ab initio complete active space self-consistent field (CASSCF) and the second order multireference Moller-Plesset calculations have been per-formed to examine the photochemical behavior of styrene upon the strong S-0-S-2 electronic excitation in the low-lying excited states. The optimized structure at the S-2/S-1, conical intersection (CIX) is characterized by a quinoid structure. The transition state (TS) in S-1 is in the vicinity of the S-2/S-1-CIX. At the S-1-TS, two reaction paths branch. One is the relaxation into the stable structure in S, and then emission into S, The other is the radiationless decay through the S-1/S-0-CIX. (C) 2002 Wiley Periodicals, Inc.