DYNAMICS OF GEMINATE CHARGE SEPARATION IN LIQUID METHYLCYCLOHEXANE STUDIED BY THE PHOTOASSISTED ION-PAIR SEPARATION TECHNIQUE

A laser photoassisted ion pair separation technique has been developed to study the kinetics of geminate charge recombination in the picosec ond domain in hydrocarbon liquids, Recombination of geminate pairs in liquid methylcyclohexane has been studied by this technique, The elect rons were created by two-photon ionization of the anthracene and tetra methyl-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 t he observed dependence of the IR enhanced photoconductivity of the sol utions on the time delay between the UV and IR pulses, The average ini tial separation between a geminate trapped electron and its sibling ca tion was obtained from the experimental decay curves of the IR enhance d photocharge. The separation in the geminate electron-cation pair was found to increase with initial excess excitation energy, Delta E, of the solute above its ionization threshold, It is concluded that the ho t electron, the precursor of the trapped geminate electron, is initial ly injected into the liquid with kinetic energy that increases with in creasing the Delta E energy.