Ab initio study on the photochemical behavior of styrene

Ab initio complete active space self‐consistent field (CASSCF) and the second order multireference Møller‐Plesset calculations have been performed 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 1 and then emission into S 0 . The other is the radiationless decay through the S 1 /S 0 ‐CIX. © 2002 Wiley Periodicals, Inc. J Comput Chem 10: 950–956, 2002