Geometrical structure of solvated electrons

Microsolvation of electrons by a handful of ammonia molecules

Microsolvation of electrons in ammonia is studied here via anionic NH_{3 n} ^- clusters with n = 2-6. Intensive samplings of the corresponding configurational spaces using second-order perturbation theory with extended basis sets uncover rich and complex energy landscapes, heavily populated by many local minima in tight energy windows as calculated from highly correlated coupled cluster methods. There is a marked energetical preference for structures that place the excess electron external to the molecular frame, effectively coordinating it with the three protons from a single ammonia molecule. Overall, as the clusters grow in size, the lowest energy dimer serves as the basic motif over which additional ammonia molecules are attached via unusually strong charge-assisted hydrogen bonds. This is a priori quite unexpected because, on electrostatic grounds, the excess electron would be expected to be in contact with as many protons as possible. Accordingly, a full quantum mechanical treatment of the bonding interactions under the tools provided by the quantum theory of atoms in molecules is carried out in order to dissect and understand the nature of intermolecular contacts. Vertical detachment energies reveal bound electrons even for n = 2.

Excess electrons in methanol clusters: Beyond the one-electron picture

We performed a series of comparative quantum chemical calculations on various size negatively charged methanol clusters, CH₃OH_n^-. The clusters are examined in their optimized geometries (n = 2-4), and in geometries taken from mixed quantum-classical molecular dynamics simulations at finite temperature (n = 2-128). These latter structures model potential electron binding sites in methanol clusters and in bulk methanol. In particular, we compute the vertical detachment energy (VDE) of an excess electron from increasing size methanol cluster anions using quantum chemical computations at various levels of theory including a one-electron pseudopotential model, several density functional theory (DFT) based methods, MP2 and coupled-cluster CCSD(T) calculations. The results suggest that at least four methanol molecules are needed to bind an excess electron on a hydrogen bonded methanol chain in a dipole bound state. Larger methanol clusters are able to form stronger interactions with an excess electron. The two simulated excess electron binding motifs in methanol clusters, interior and surface states, correlate well with distinct, experimentally found VDE tendencies with size. Interior states in a solvent cavity are stabilized significantly stronger than electron states on cluster surfaces. Although we find that all the examined quantum chemistry methods more or less overestimate the strength of the experimental excess electron stabilization, MP2, LC-BLYP, and BHandHLYP methods with diffuse basis sets provide a significantly better estimate of the VDE than traditional DFT methods (BLYP, B3LYP, X3LYP, PBE0). A comparison to the better performing many electron methods indicates that the examined one-electron pseudopotential can be reasonably used in simulations for systems of larger size.

Time- and space-resolved Monte Carlo study of water radiolysis for photon, electron and ion irradiation

Time-dependent yields of the most important products of water radiolysis E(aq)(-), (*)OH, H(*), H(3)O(+), H(2), OH(-) and H(2)O(2) have been calculated for (60)Co-photons, electrons, protons, helium- and carbon-ions incident onto water. G values have been evaluated for the interval from 1 ps to 1 mus after initial energy deposition as a function of time, as well as after 1 ns and at the end of the chemical stage as a function of linear energy transfer (LET), covering an interval from approximately 0.2 up to 750 keV/microm by means of different particle types. In this work, the modules of the biophysical Monte Carlo track structure code PARTRAC dealing with the simulation of prechemical and chemical stages have been improved to extend interaction data sets for heavier ions. Among other newly selected parameter values, the thermalisation distance between the point of generation and hydration of subexcitation electrons has been adopted from recent data in the literature. As far as data from the literature are available, good agreement has been found with the calculated time- and LET-dependent yields in this work, supporting the selection of the revised parameter values.

Vibrational spectroscopy of hydrated electron clusters(H2O)15–50− via infrared multiple photon dissociation

Infrared multiple photon dissociation spectra for size-selected water cluster anions (H2O)(n)(-), n=15-50, are presented covering the frequency range of 560-1820 cm(-1). The cluster ions are trapped and cooled by collisions with ambient He gas at 20 K, with the goal of defining the cluster temperature better than in previous investigations of these species. Signal is seen in two frequency regions centered around 700 and 1500-1650 cm(-1), corresponding to water librational and bending motions, respectively. The bending feature associated with a double-acceptor water molecule binding to the excess electron is clearly seen up to n=35, but above n=25; this feature begins to blueshift and broadens, suggesting a more delocalized electron binding motif for the larger clusters in which the excess electron interacts with multiple water molecules.