Intersystem crossing in tunneling regime: T1 → S0 relaxation in thiophosgene. Issue 10 (26th February 2020)

• Record Type: Journal Article
• Authors: Lykhin, Aleksandr O.; Varganov, Sergey A.
• Is Part Of: Physical chemistry chemical physics. Volume 22:Issue 10(2020)
• Page Start: 5500
• Page End: 5508
• Publication Date: 2020-02-26
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c9cp06956a
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : The nonadiabatic transition state theory provides insight into the T1 → S0 intersystem crossing in thiophosgene driven by quantum tunneling through the barrier formed by the crossing T1 and S0 electronic states. Abstract : The T1 excited state relaxation in thiophosgene has attracted much attention as a relatively simple model for the intersystem crossing (ISC) transitions in polyatomic molecules. The very short (20–40 ps) T1 lifetime predicted in several theoretical studies strongly disagrees with the experimental values (∼20 ns) indicating that the kinetics of T1 → S0 ISC is not well understood. We use the nonadiabatic transition state theory (NA-TST) with the Zhu–Nakamura transition probability and the multireference perturbation theory (CASPT2) to show that the T1 → S0 ISC occurs in the quantum tunneling regime. We also introduce a new zero-point vibrational energy correction scheme that improves the accuracy of the predicted ISC rate constants at low internal energies. The predicted lifetimes of the T1 vibrational states are between one and two orders of magnitude larger than the experimental values. This overestimation is attributed to the multidimensional nature of quantum tunneling that facilitates ISC transitions along the non-minimum energy path and is not accounted for in the one-dimensional NA-TST.