Dynamics of excess electrons in atomic and molecular clusters

Femtosecond time-resolved photoelectron imaging (TRPEI) is applied to the study of excess electrons in clusters as well as to microsolvated anion species. This technique can be used to perform explicit time-resolved as well as one-color (single- or multiphoton) studies on gas phase species. The first part of this dissertation details time-resolved studies done on atomic clusters with an excess electron, the excited-state dynamics of solvated molecular anions, and charge-transfer dynamics to solvent clusters. The second part summarizes various one-color photoelectron imaging studies on tetrahydrofuran clusters with an excess electron or doped with an iodide ion in order to probe the solvent structure of these clusters. Finally, a mixed study is presented exploring the effect of warmer cluster conditions on both the binding energies and relaxation times of excess electrons in water clusters.;Time-resolved studies on mercury cluster anions (Hg)n ¯ (7 ≤ n ≤ 20) demonstrate the different timescales of electron-phonon and electron-electron scattering in small systems. Low-energy (1.0--1.5 eV) excitation of the excess electron to a higher-lying electronic state decays via a cascade through the conduction band on a 10--40 ps timescale. Conversely, high-energy (4.7 eV) excitation of an electron from the valence band into the conduction band opens a second relaxation pathway: emission of the excess electron via Auger decay. The larger number of charge carriers and the geometrical changes to the cluster following the creation of the valence band hole state increase the relaxation rate, causing relaxation to occur on a 100s of fs timescale. The size dependence of both relaxation timescales becomes much less significant around n = 13 near the van der Waals-to-covalent bonding transition seen in other studies of mercury clusters.;Electron solvation dynamics following charge-transfer-to-solvent excitation from iodide to small methanol clusters, I(CH3OH) n (4 ≤ n ≤ 11) are also examined with TRPEI. After electron transfer, the excited state spectrum undergoes significant evolution in both its position and shape. Considerations of the geometries of the initial iodide-doped methanol cluster as well as the intermediate bare methanol anion cluster and final neutral clusters suggest the electron is solvated, as at least one methanol molecule rotates to bring its hydroxyl group inward toward the cluster center, maximizing the hydrogen bond network. The observed relaxation timescales for both the vertical detachment energies and the spectral width (5--30 ps) are consistent with this type of motion. An autodetachment feature is also observed at all pump-probe delays, indicating that this is the primary decay pathway for these clusters, which is consistent with the lack of observed stable methanol cluster anions in this size range.;One-color, one photon photoelectron imaging is applied to study tetrahydrofuran cluster anions (THF)n ¯ (1 ≤ n ≤ 100) to probe the nature of the solvated electron in that solvent. An anion at the same mass-to-charge ratio as the THF anion is observed, though THF¯ is not expected due to its closed shell electronic structure, high HOMO-LUMO gap and dipole moment. Two peaks are observed in the photoelectron spectrum for this species, one of which is attributed to a long-chain C 4H8O anion formed after ring-opening from the secondary electron attachment. The other peak is likely due to a metastable THF transient negative ion arising from fragmentation of the larger clusters. These features persist until n = 5. By n = 6, the photoelectron spectra change shape, becoming much larger, and maintain that shape through n = 100. This transition is accompanied by an abrupt change in the photoelectron angular distribution. These changes are attributed to onset of the solvated electron state in THF clusters. The binding energy for the smallest cluster of this species is 1.96 eV, much higher than that for other solvated electron clusters at onset. Extrapolation to infinite cluster sizes yields a bulk value of 3.10 +/- 0.03 eV. The energetics are analyzed in the frameworks of dielectric continuum theory and the proposed cavity structure for bulk THF. (Abstract shortened by UMI.)...