Charge Transfer Dynamics in Dissociation of Halomethanes induced by Extreme Ultraviolet Free-Electron Lase

Electron transfer plays an important role in chemical bond formation and cleavage and is related to electron delocalization and localization. Ultrafast electron transfer in the dissociative ionization of CH₃I and CH₂ICl was investigated at FLASH2 by an extreme ultraviolet (EUV) pump-probe experiment. The charge transfer is traced by the yields of the dicationic species as a function of delay between the two EUV pulses. An exponential dependence of charge transfer on the internuclear distance is observed, which shows considerable deviation from the classical over-the-barrier model. Considering the thermal energy of the electrons, we develop a semi-classical model based on a reaction rate equation that quantitatively reproduces the observed behavior at sufficiently large internuclear separations.