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 (³Π) of ClF are probed and the dynamics for excitation to the singlet state (¹Π₁) is compared with excitation to the triplet state B(³Π₀). The population initially excited to the singlet state ¹Π₁ is transferred to the bound triplet states ³Π within τ_f=0.5  ps. 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 F₂/Ar, 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, 40% of the triplet population accumulates in the weakly bound ³Π states, in good accord with the experiment.