Ultrafast Solvent-Induced Spin-Flip and Nonadiabatic Coupling: ClF in Argon Solids

Femtosecond pump-probe spectra show direct evidence for ultrafast solvent-induced spin flip in photodissociation-recombination events of ClF, a light diatomic molecule, for which the spin-orbit coupling is weak. The bound triplet states [Formula presented] of ClF are probed and the dynamics for excitation to the singlet state [Formula presented] is compared with excitation to the triplet state [Formula presented]. The population initially excited to the singlet state [Formula presented] is transferred to the bound triplet states [Formula presented] within [Formula presented]. Oscillations in the spectra indicate wave packet dynamics with the triplet state period of 300 to 400 fs in both cases. According to simulations of [Formula presented], most of the initially excited singlet state population is converted to repulsive and weakly bound triplet states within approximately 60 fs. In the first ps, [Formula presented] of the triplet population accumulates in the weakly bound [Formula presented] states, in good accord with the experiment.