No abstract

Ultrafast charge carrier dynamics in graphite has been investigated by time-resolved terahertz spectroscopy. Analysis of the transient dielectric function and model calculations show that more than 90% of the initially deposited excitation energy is transferred to a few strongly coupled lattice vibrations within 500 fs. These hot optical phonons also substantially contribute to the striking increase of the Drude relaxation rate observed during the first picosecond after photoexcitation. The subsequent cooling of the hot phonons yields a lifetime estimate of 7 ps for these modes.

Electron solvation dynamics in photoexcited anion clusters of I-(D2O)n=4-6 and I-(H2O)4-6 were probed by using femtosecond photoelectron spectroscopy (FPES). An ultrafast pump pulse excited the anion to the cluster analog of the charge-transfer-to-solvent state seen for I- in aqueous solution. Evolution of this state was monitored by time-resolved photoelectron spectroscopy using an ultrafast probe pulse. The excited n = 4 clusters showed simple population decay, but in the n = 5 and 6 clusters the solvent molecules rearranged to stabilize and localize the excess electron, showing characteristics associated with electron solvation dynamics in bulk water. Comparison of the FPES of I-(D2O)n with I-(H2O)n indicates more rapid solvation in the H2O clusters.

The femtosecond dynamics of localization and solvation of photoinjected electrons in ultrathin layers of amorphous solid H2O and D2O have been studied by time- and angle-resolved two-photon-photoelectron spectroscopy. After electron transfer from the metal substrate into the conduction band of ice, the excess electron localizes within the first 100 fs in a state at 2.9 eV above E(F), which is further stabilized by 300 meV on a time scale of 0.5-1 ps due to molecular rearrangements in the adlayer. A pronounced change of the solvation dynamics at a coverage of approximately 2 bilayers is attributed to different rigidity of the solvation shell in the bulk and near the surface of ice.