Chapter 51 - Electronic solvation dynamics in non-polar supercritical fluids

Abstract

Solvation dynamics is usually investigated by following in “real time” the response of the medium to an impulsive redistribution of charge of a solute. Experimentally, short pulse excitation of a chromophore creates instantaneously a “new” molecule, to which the surrounding solvent molecules respond. Contrary to liquids, studies of non-polar solvation dynamics in supercritical fluids (SCFs) are very rare and a molecular level description of the solvation process is still needed. In particular, the strong local density fluctuations appearing near the critical point, which are responsible for most of the unusual solvation properties of SCFs, may influence significantly the solute-solvent structural and dynamical properties. This chapter investigates SC Argon as a model non-polar solvent. Rydberg states are used to get an insight into the non-polar solvation dynamics. This chapter investigates, experimentally, steady-state (absorption and fluorescence) spectroscopy of the Rydberg transition over a wide range of thermodynamical conditions in the Ar supercritical (SC) domain. Then, molecular dynamics (MD) simulations, whose validity is checked by reproducing the steady-state spectroscopic observables, are used to explore the details of structural rearrangements and solvation dynamics upon excitation of a Rydberg state. In particular, the influence of the near-critical local density fluctuations on solvation dynamics is analyzed.