Energy Of Quasi-free Electron Research Articles

Energy of the quasi-free electron in CO and HD: Probing intermolecular potentials within the local Wigner-Seitz model.

We present the quasi-free electron energy V0(ρ) in the weakly polar fluids CO and HD from gas to liquid densities ρ, on noncritical isotherms, and at a temperature near the critical isotherm. These results represent the first systematic investigation of V0(ρ) in polar fluids across a broad density range and illustrate that field enhanced photoemission can be used to obtain data in such systems. We show that the local Wigner-Seitz model for V0(ρ), when coupled with thermodynamic data for the fluids, can yield optimized intermolecular potential parameters, as well as the magnitude of the zero kinetic energy electron scattering length.

Energy of the quasi-free electron in H2, D2, and O2: Probing intermolecular potentials within the local Wigner-Seitz model.

We present for the first time the quasi-free electron energy V0(ρ) for H2, D2, and O2 from gas to liquid densities, on noncritical isotherms and on a near critical isotherm in each fluid. These data illustrate the ability of field enhanced photoemission (FEP) to determine V0(ρ) accurately in strongly absorbing fluids (e.g., O2) and fluids with extremely low critical temperatures (e.g., H2 and D2). We also show that the isotropic local Wigner-Seitz model for V0(ρ)--when coupled with thermodynamic data for the fluid--can yield optimized parameters for intermolecular potentials, as well as zero kinetic energy electron scattering lengths.

The energy of the quasi-free electron in near critical point nitrogen

Field enhanced photoemission is used to measure the density dependent quasi-free electron energy V0(ρ) in the strongly absorbing gas N2 for the first time. V0(ρ) in N2 was obtained from low density to the density of the triple point liquid, at noncritical temperatures and on an isotherm near the critical isotherm. A novel critical point effect is observed and is accurately explained by the local Wigner–Seitz model.

Quasi-free electron energy in near critical point helium

We present for the first time the quasi-free electron energy V0(ρ) in helium from low density to the density of the triple point liquid (gaseous helium/liquid helium I/liquid helium II triple point), on a noncritical isotherm and on an isotherm near the critical temperature. These data were obtained using field enhanced photoemission, a new experimental technique for the characterization of dense fluids. A novel critical point effect in helium is presented and is accurately fitted to the local Wigner–Seitz model. This model, which was developed for attractive fluids, is thereby shown to be applicable to repulsive fluids as well.

Field enhanced photoemission: A new technique for the direct determination of the quasi-free electron energy in dense fluids

Previous experimental studies of the quasi-free electron energy V 0 ( ρ ) in dense fluids either directly measured V 0 ( ρ ) , using photoemission from an electrode immersed in the fluid, or extracted V 0 ( ρ ) from field ionization of a dopant dissolved in the fluid. In this letter, we present a new method to determine directly V 0 ( ρ ) , namely field enhanced photoemission. We show that this new method yields data comparable to those obtained from dopant field ionization, thereby making this method superior to direct photoemission studies. Moreover, unlike dopant field ionization, field enhanced photoemission is not limited by the solubility of a dopant in the fluid of interest.

Density dependence of the ionization potential of CH3I in krypton and of the quasi-free electron energy in krypton

Field ionization has been employed to determine the ionization potential of CH3I doped in krypton for krypton densities between the gas and the triple point liquid. The ionization potential is correlated to the different configurations of the host atoms around the dopant at the moment of excitation and is, therefore, represented by a distribution. The ion-medium polarization energy distribution was calculated, from the first and second moments, at the densities at which the experiments were performed. The calculated widths are in very good agreement with those of the experimentally determined ionization potentials. By combining the experimental results with those of the calculations, the density dependence of the quasi-free electron energy in Kr was determined. These results are compared to those obtained in previous experiments and with recent theoretical calculations.

Ermittlung der elektronenaffinität von methylenblau aus dem photoionisationspotential von methylenblau-radikal in hexan

Photoionization threshold energy of methylene-blueradical IE(MB ) th in n-hexane was determined by measuring the photocurrent to be 5,1 ev. Adding the polarization energy and the energy of quasi-free electron to this value the resulting energy agrees with electron affinity of methyleneblue which has been calculated to EA(MB + ) = IE(MB + ) - ΔE 1 (MB + ) = 5,8 ev and previously from polarographic and calorimetric measurements. Threshold energy for photoonization according to [MB + …e] → [MB 2+ …2e] was determined to be 6,7 ev.

Dependence of specific rates for excess-electron scavenging in nonpolar liquids on electron energy

Electron scavenging reactions in nonpolar molecular liquids exhibit anomalous solvent effects which appear to depend principally upon V/sub 0/, the quasi-free electron energy. The rate constant k/sub s/ will be described in terms of the following general mechanism: (1, -1) e/sup -/ + A in equilibrium (e/sup -/, A) and (2) (e/sup -/, A) ..-->.. X/sup -/, where X/sup -/ is the stabilized product for either dissociative or nondissociative attachment. Important variations of the general kinetic scheme are due in part to the electron transport mechanism and the state of the reacting electron, including its energy. In neopentane, e.g., a gaslike mechanism of collisions is proposed, inefficient acceptors requiring thermal activation. It is necessary to distinguish between electron potential energy and kinetic energy. For an efficient acceptor k/sub s/ proportional to k/sub 1/ is approximately constant in all high-mobility media. The trap model and the hopping model determine kinetic differences which are quite distinguishable in principal but not yet resolved in practice. Both k/sub s/ = b..mu.. with b constant and k/sub s/ proportional to ..mu../sup n/ for 0 < n < 1 follow from the general scheme. Most results are expressible in terms of (b..mu../k/sub s/ - 1)/sup -1/more » = k/sub 2//k-/sub 1/ with k/sub 2/ depending exponentially on temperature.« less

Comments on the magnitude and sign of the quasifree electron energy in the rare-gas solids as inferred from ESR studies of Frenkel impurity states

We point out that the magnetic properties of tightly-bound H atom impurities in dense, nonpolar solids are sensitive not only to local contributions to an effective potential, but also to electron– (bulk) medium interactions which dictate the nature of the ground state of an excess electron in these materials.

Field emission into nonpolar organic liquids

Field emission into nonpolar liquids was studied for n-hexane, 2,2,4-trimethylpentane, and tetramethylsilane at 275–334 K. The current–voltage dependence was found to vary depending on the liquids and the temperature, and was reproduced qualitatively on the basis of the Fowler–Nordheim theory modified by taking account of the space charge effect. The quasifree electron energy (the electron energy in a liquid with reference to that in vacuum) was estimated from the current–voltage dependence in a space charge-free region, i.e., from the apparent work functions of the metal emitter (tungsten tip) in the liquids, to be 0, −0.6, and −1.3 eV for n-hexane (as a standard), trimethylpentane, and tetramethylsilane, at 293 K. These values lie in the same order as determined previously by the photoelectric emission from a metal surface in the liquids, though the dependence on the liquids is more pronounced in the present field emission study.

Radiation chemical yield and mobility of electrons in liquid hydrocarbons

Geminate ion-electron recombination is reconsidered theoretically and compared with the experimentally observed interdependence between free ion yield, G fi and electron mobility, μ or quasi-free electron energy, V 0. Thermal electrons are regarded as being formed in the quasi-free state, hence their motion can be described as that of a spherical wave with the geminate positive ion in the centre. One can show that the escape probability of thermal quasi-free electrons equals about one-half in each and any system if electron scattering by the molecules is neglected. Further, it is assumed that the escaped fraction of quasi-free electrons partially localize in the liquid. In this second stage of their life localized electrons behave as heavy particles in that they obey Onsager's recombination law. The distribution of distances between ions and localized electrons, an essential function in the Onsager theory, can be expressed in terms of trapping probability which is a function of either V 0 or μ. Calculated G fi( V 0) and G fi(μ) curves adequately agree with experiment. The last time that I had the chance of attending a lecture given by Robert L. Platzman was during the 4th International Congress of Radiation Research at Evian in 1970. Having been unable to read the text of that talk I have to rely on my memory in recalling the cardinal points of his arguments. So it is difficult for me to tell which ideas of the present paper stem directly from him. It is, however, beyond doubt that it was at his instigation, direct and indirect, that I decided to tackle the problems discussed below.

Application of the Semicontinuum Model to Pressure Effects on Solvated Electron Spectra in Methanol and Ethanol

The semicontinuum model for solvated electrons has been applied to the calculation of pressure effects on solvated electron spectra in methanol and ethanol at 298°K. The pressure dependence of the density, static, and optical dielectric constants and the quasifree electron energy state have all been included. The calculated results satisfactorily explain the experimentally observed blue shifts with pressure. Analysis shows that pressure affects short range interactions much more than long range interactions and results in a decrease in the electron cavity radius and an increase in the energy of the quasifree electron state.

A semi-empirical estimate of the scattering cross section and mobility of excess electrons in liquid hydrocarbons

The scattering cross sections and intrinsic mobility of electrons in liquid hydrocarbons have been calculated from measurements of the quasi-free electron energy. By incorporating the mobility temperature dependence the calculated mobilities satisfactorily explain the tenfold difference of mobilities in n-hexane and neopentane.