Ultrafast nuclear dynamics of the acetylene cation C2H2+ and its impact on the infrared probe pulse induced C–H bond breaking efficiency

Abstract

The ultrafast nuclear dynamics of the acetylene cation C₂H₂⁺ following photoionization of the neutral molecule is investigated using an extreme-ultraviolet pump/infrared probe setup. The observed modulation of the C₂H⁺ fragment ion yield with pump–probe delay is related to structural changes induced by the extreme-ultraviolet pump pulse taking place on the femtosecond timescale. High-level simulations suggest that the trans-bending and C–C bond stretching motion of the C₂H₂⁺ cation govern the observed interaction with the infrared pulse. Depending on the molecular configuration at arrival of the infrared pulse, it either transfers population to higher-lying states or to the C₂H₂⁺ ground state, thereby enhancing or lowering the C₂H⁺ yield. Our ultrafast pump–probe scheme can thus be used to track excited state nuclear dynamics with a resolution of a few femtoseconds, leading the way to studying fast dynamics also in larger hydrocarbon molecules.