Dynamics of geminate charge separation in liquid methylcyclohexane studied by the photoassisted ion pair separation technique Original Research Article

A laser photoassisted ion pair separation technique has been developed to study the kinetics of geminate charge recombination in the picosecond domain in hydrocarbon liquids. Recombination of geminate pairs in liquid methylcyclohexane has been studied by this technique. The electrons were created by two-photon ionization of the anthracene and tetramethyl-p-phenylenediamine (TMPD) admixture using a picosecond UV laser pulse at 270 or 360 nm and then were excited by an IR laser pulse at 1080 nm. The diffusion model of photostimulated ion pair dissociation has been extended to the picosecond time regime in order to describe the observed dependence of the IR enhanced photoconductivity of the solutions on the time delay between the UV and IR pulses. The average initial separation between a geminate trapped electron and its sibling cation was obtained from the experimental decay curves of the IR enhanced photocharge. The separation in the geminate electron-cation pair was found to increase with initial excess excitation energy, ΔE, of the solute above its ionization threshold. It is concluded that the hot electron, the precursor of the trapped geminate electron, is initially injected into the liquid with kinetic energy that increases with increasing the ΔE energy.