The effect of molecular distortions on spin-orbit coupling in simple hydrocarbons

TJ Penfold, Graham Worth

Research output: Contribution to journalArticle

39 Citations (Scopus)


Recent work [D.N.S. Parker et al., Chem. Phys. Lett. 469 (2009) 43-49] has found intersystem crossing (ISC) on an ultrafast timescale in electronically excited benzene, a surprise as hydrocarbons generally have small spin-orbit coupling. In this paper, the effect of molecular distortions on spin-orbit coupling (SOC) is calculated for cyclobutadiene and benzene. At equilibrium the SOC in both molecules is negligible, and therefore terms arising from molecular distortions must play a significant role in any fast ISC. We show that out-of-plane C-H bends, which leads to the hybridisation of sigma and pi orbitals, are responsible for the most significant effect. The S-1/S-0 conical intersection is an important feature for understanding the photochemistry of these molecules. We examine the SOC along the vector from the Franck-Condon point to the lowest energy point on the crossing seam and discuss the potential importance of the SOC to the ultrafast dynamics. (C) 2010 Elsevier B.V. All rights reserved.
Original languageEnglish
Pages (from-to)58-66
Number of pages9
JournalChemical Physics
Issue number1
Publication statusPublished - 1 Sept 2010


  • Spin-orbit coupling
  • Ultrafast photochemistry
  • Conical intersections


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