Thomas Goulet

On the electronic structure of liquid water: Conduction-band tail revealed by photoionization data

Abstract The photoionization yield curves as a function of photon energy Eph of pure water or dilute aqueous solutions display an exponential behavior in the ionization threshold region. This suggests that these curves reflect the existence of an Urbach tail lying below the conduction-band edge of water. A quantitative treatment of various reported photoionization data provides an experimental basis for the determination of the energy distribution of electron trap states in the conduction-band tail of water and presents a picture of the electronic structure of liquid water which is coherent with previous results of photoelectron emission spectroscopy.

On the validity of the independent reaction times approximation for the description of the nonhomogeneous kinetics of liquid water radiolysis

Abstract The validity of using the independent reaction times (IRT) method to describe the nonhomogeneous reaction kinetics of complex and spatially correlated systems, such as ionising radiation track segments in liquid water, is tested. The time-dependent yields of various radiolytic species obtained with the IRT method are shown to compare well to those of a full step-by-step Monte Carlo simulation code. The good agreement between the two methods still holds as the linear energy transfer of the radiation is increased from 0.3 to 45 keV μm −1 .

On the relaxation kinetics following the absorption of light by solvated electrons in polar liquids: roles of the continuous spectral shifts and of the stepwise transition

Abstract The relaxation kinetics that is observed to follow the absorption of 780-nm light by fully solvated electrons in water and in various alcohols is re-analysed. The present investigation aims at assessing the respective roles played in such three-pulse experiments by (i) the stepwise transition between a weakly bound and a strongly bound electron–solvent configuration and (ii) the continuous spectral shifts of the transient spectra of those two species. In particular, the suggestion of Walhout et al. [Walhout, P.K., Alfano, J.C., Kimura, Y., Silva, C., Reid, P.J., Barbara, P.F., 1995. Direct pump/probe spectroscopy of the near-IR band of the solvated electron in alcohols. Chem. Phys. Lett., 232, 135.] that the stepwise transition is as short (

Monte carlo simulations of low-energy (<10eV) electron transmission and reflection experiments: application to solid xenon

A Monte Carlo method is developed for simulating low-energy (< 10 eV) electron-impact transmission and reflection experiments. This method is applied to test the results obtained with various electron transport models which have recently been proposed for the interpretation of these experiments on thin solid xenon films. Particular attention is given to the critical examination of the adequacy of the assumption of isotropy of the collisions which is generally used in these models to calculate the various electron transport parameters, such as the elastic and inelastic electron scattering mean free paths. The simulation is also used to predict both the variation of the electron current transmitted through the films with the incident angle of the electron beam and the angular distribution of the reflected electrons.

Linear-energy-transfer effects on the radiolysis of liquid water at temperatures up to 300°C : a Monte-Carlo study

Abstract Monte-Carlo simulations are used to calculate the primary radical and molecular yields (g-values) of water radiolysis versus temperature in the range 25–300°C, for different high linear energy transfer radiations (protons, 2 H + , and 7 Li 3+ ) up to ∼ 65 keV / μm . The results are compared, at ∼10−7 s, to experimental data at 25°C, 95°C, and 180°C. Excellent agreement is obtained for g(e−aq) and g( OH ) over the whole temperature range, but g(H2), [g(H )+g(H2)], and g(H2O2) are substantially larger than the measured values at 180°C. Our g-values are also compared with fast-neutron radiolysis yields and with deterministic modeling calculations. The agreement is generally satisfactory.

A procedure for determining low-energy (<10eV) electron mean free paths in molecular solids: benzene

Abstract A procedure is presented which can be used to estimate the energy-dependent values of the various relevant low-energy (

Theoretical study of the transmission of low-energy (0–10 eV) electrons through thin-film organic molecular solids: Benzene

Abstract A theoretical study of the transmission of low-energy (0–10 eV) electrons incident from vacuum through thin-film organic molecular solids deposited on a cold metal substrate is presented and developed for the specific case of solid benzene. In essence, using a semiclassical description of electron transport in solids with an energy-independent scattering mean free path and assuming an isotropic electron scattering, the behavior of a penetrating electron in the film is simulated when a large number of scattering events are present. The good agreement between the calculated electron transmission spectra and those obtained experimentally indicates that our study provides a realistic description of the electron transport in the film, and accounts for the influence of the various electron-molecule scattering processes upon the energy dependence of the transmitted current. In particular, we show that the excitonic subionization energy losses are at the origin of the main structures of the observed electron transmission spectra. It is also shown that our study can successfully be used to estimate the probabilities of the various electron scattering processes which occur in the film, as well as the electron mean free path l. For solid benzene, l is about 8 A in the considered electron energy range.

Analysis of low-energy (1–10 ev) electron transmission spectra of thin solid krypton films

Abstract We present and analyse the results of low-energy electron transmission experiments performed with solid krypton films deposited on a platinum substrate at 20 K. The film thicknesses range from about 0.3 to 10 nm. The analysis of the variation of the transmitted electron current with film thickness is done with the help of a probabilistic model of particle transport in the energy region (1–10 eV) where the electron scatterings are quasi-elastic. This analysis allows the determination of the entrance probability of electrons and their mean free path in the films. The entrance probability is found to reflect the electronic conduction-band structure of solid krypton. The electron mean free path values that we obtain are large for low electron energies (about 20 nm at 1 eV) and decrease rapidly to about 2 nm for energies larger than 3.5 eV.