## Abstract

Spin-orbit coupling (SOC) induced intersystem crossing (ISC) has long been believed to play a crucial role in determining the product distributions in the O(^{3}P) + C_{2}H_{4} reaction. In this paper, we present the first nonadiabatic dynamics study of the title reaction at two center-of-mass collision energies: 0.56 eV, which is barely above the H-atom abstraction barrier on the triplet surface, and 3.0 eV, which is in the hyperthermal regime. The calculations were performed using a quasiclassical trajectory surface hopping (TSH) method with the potential energy surface generated on the fly at the unrestricted B3LYP/6-31G(d,p) level of theory. To simplify our calculations, nonadiabatic transitions were only considered when the singlet surface intersects the triplet surface. At the crossing points, Landau-Zener transition probabilities were computed assuming a fixed spin-orbit coupling parameter, which was taken to be 70 cm^{-1} in most calculations. Comparison with a recent crossed molecular beam experiment at 0.56 eV collision energy shows qualitative agreement as to the primary product branching ratios, with the CH_{3} + CHO and H + CH_{2}CHO channels accounting for over 70% of total product formation. However, our direct dynamics TSH calculations overestimate ISC so that the total triplet/singlet ratio is 25:75, compared to the observed 43:57. Smaller values of SOC reduce ISC, resulting in better agreement with the experimental product relative yields; we demonstrate that these smaller SOC values are close to being consistent with estimates based on CASSCF calculations. As the collision energy increases, ISC becomes much less important and at 3.0 eV, the triplet to singlet branching ratio is 71:29. As a result, the triplet products CH_{2} + CH_{2}O, H + CH_{2}CHO and OH + C_{2}H_{3} dominate over the singlet products CH_{3} + CHO, H_{2} + CH _{2}CO, etc.

Original language | English |
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Pages (from-to) | 2093-2103 |

Number of pages | 11 |

Journal | Journal of Physical Chemistry A |

Volume | 112 |

Issue number | 10 |

DOIs | |

Publication status | Published - Mar 13 2008 |

## ASJC Scopus subject areas

- Physical and Theoretical Chemistry