Ultraviolet charge-transfer-to-solvent (CTTS) bands are general spectral features of inorganic salts dissolved in dipolar (e.g., aqueous) solvents. The bands originate from excitations of the anions, and the excited states are thought to involve a delocalized electronic state supported by the arrangement of solvent molecules around the ion in the ground state. These diffuse states have fascinated physical chemists since the 1930s, who first used continuum models to explain the phenomenon and then later refined the treatment to include local molecular interactions. In this paper, we report that CTTS bands evolve from features present in very small gas phase clusters, I−⋅(H2O)n, n=1–4, and discuss how localization of the continuum wave function of the ejected electron acts as a precursor to the bound excited state in the liquid.

Optical Investigations Into the relative role of Penning Ionization as a mechanism for the Ionization of sputtered species In low-pressure argon glow discharges were carried out. These studies employed methane as a quenching agent to effectively reduce the argon metastable population. This reduction of metastable atoms significantly limits the extent of Penning Ionization present In the discharge, which will decrease ion emission signals from the sputtered species. The magnitude of the decrease In these Ion emission signals may then be related to the relative importance of the Penning Ionization process In overall discharge Ionization of the sputtered species. These studies show Penning ionization to account for approximately 40-80% of the ionization of sputtered species, depending upon discharge conditions of current and pressure.

Resonant vibration-vibration energy transfer between highly vibrationally excited O2(X 3Σ− g ,v=15-26) and CO2, N2O, N2, and O3We report the observation of resonance structure in the photodetachment spectrum of O 2 Ϫ in the 4 eV range, which results from the excitation of autodetaching vibrational levels of the O 2 Ϫ A -X transition near the dissociation limit. The evolution of the resonances with increasing vibration is simply explained using continuity of the inner part of the vibrational wave functions across the dissociation threshold. This affords the possibility of investigating the DA process at the half-collision, in a kind of ''correspondence limit'' where the outer turning point slowly recedes and the vibrational wave function incrementally adopts the character of the dissociation continuum. Photoexcitation near one of the resonances results in the population of significantly higher vibrational levels in the O 2 a 1 ⌬ g state ͑which are cleanly resolved͒ than the typical ''Franck-Condon'' pattern observed for nonresonant photodetachment. Finally, hot-band structure is also observed in the detachment spectrum, allowing us to extract a more accurate value of the O 2 Ϫ vibrational quantum (⌬Gϭ134.4Ϯ0.8 meV͒ by about an order of magnitude over previous determinations.

We report the branching ratios, #, for photodissociation of 0 2 -in water clusters, 02-*(H~0)~, as a function of excess energy [over the bond energy, E,,,,,, = hv -D0(02-)] and cluster size, 1 I n I 33. The twodimensional #(Eexcess, n) "dissociation" surface is generated from a series of measurements over the range 0 I E,,,,,, I 1.8 eV and displays features attributable to attractive forces at small E,,,,,, and repulsive interactions at high E,,,,,,. This #(Eexcess, n) surface is essentially independent of cluster size in the range 18 I n I 33, where all clusters are characterized by a single #(Eexcess) curve. Similarly, #(Eexcess, n) becomes independent of E,,,,,, at high E,,,,,, (21 eV) with a characteristic #(n) dependence. At both large E,,,,,, and large n, #(Eexcess, n) displays a plateau at about 0.70 which is very weakly dependent on both E,,,,,, and n. We interpret the shape of the surface in the context of a model recently developed by Apkarian and co-workers (J. Phys. Chem. 1994,98,7966) to explain the excess energy-dependent dissociation yields for small molecules in rare-gas matrices.