The role of rotational relaxation in the intersystem crossing between a triplet and a singlet electronic state

A calculation of the rate of ISC (intersystem crossing) relaxation at 0 K requires a knowledge of the spin–orbit coupling and the vibrational overlap integrals (Franck-Condon factors) between the T1 and S0 states. At elevated temperatures, the population of the rotational states needs to be taken into account through the overlap of the rotational wavefunctions between the interacting T1/S0 electronic states. Here, we discuss the effect of the ISC singlet–triplet selection rules on the number and magnitude of the rotational overlap factors for the J = 0, 5, and 10 rotational levels of thiophosgene, Cl2CS. Of equal importance is the influence of the spin–spin and spin-rotation coupling on the rotational fragmentation factors and the ISC survival probability. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011