Ultrafast Ring-Opening Dynamics of 1,2-Dithiane Following Ultraviolet Absorption

We report results from a recent laser pump–probe study into the ultrafast ring-opening dynamics of 1,2-dithiane. Following absorption of a 290 nm photon, the nuclear dynamics were probed as a function of pump–probe delay on the femtosecond timescale by strong-field ionisation with an 800 nm probe pulse, resulting in production of a range of atomic and molecular fragment ions. The time-dependent yields of atomic fragment ions reveal evidence of coherent nuclear wavepacket dynamics corresponding to the previously proposed ‘Newton's cradle’ motion of 1,2-dithiane, in which repeated ring opening, structural inversion, and ring closing occurs on a timescale of ∼400-500 fs. Based on surface-hopping trajectory simulations of the non-adiabatic dynamics, we are able to rationalise the observed time-dependent ion yields in terms of a geometry-dependent variation in ionisation energy for the photoexcited 1,2-dithiane molecule.