The nonadiabatic statistical theory (NAST) predicts the probabilities and rate constants of intersystem crossing (ISC) transitions between the electronic states with different spin multiplicities. NAST assumes that the ISC transitions driven by the spin-orbit coupling (SOC) happen in the vicinity of a minimum energy point on the crossing seam between these electronic states. We extend the NAST capabilities by considering effects of an external magnetic field on the ISC kinetics, including the higher-order spin-orbit-Zeeman interaction. Our results demonstrate that without SOC, magnetic field cannot facilitate the ISC transitions between singlet and triplet states. Application of an external magnetic field breaks the degeneracy of MS components of the triplet state producing distinct couplings between the singlet state and each MS component of the triplet state. These distinct couplings affected by an external magnetic field lead to different ISC rate constants for transitions between different MS components. Detailed understanding of these interstate couplings will facilitate the development of the mechanisms to control chemical reactions at ISC with an external magnetic field.

Nonadiabatic statistical theory with an external magnetic field

ACS Spring 2022

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