M.-T. Lee

A comparative experimental-theoretical study on elastic electron scattering by methane

Absolute differential cross sections for elastic electron scattering by methane have been measured at six incident electron energies between 5 and 100 eV and over scattering angles between 10° and 180°, using a crossed-beam electron spectrometer combined with a magnetic angle-changing device to extend the measurements to backward angles (125°–180°). Differential, integral and momentum-transfer cross sections are also calculated and reported for these energies. A complex optical potential was used to represent the electron–molecule interaction dynamics. The iterative Schwinger variational method combined with the distorted-wave approximation was used to solve the scattering equations. The comparison between our calculated and measured results, as well as with other experimental and theoretical data available in the literature, is encouraging.

Elastic and total cross sections for electron-carbon dioxide collisions in the intermediate energy range

In this work, we report on a joint theoretical and experimental investigation on electron-CO2 collisions in the intermediate energy range. More specifically, the elastic differential, integral and momentum transfer cross sections as well as the grand total (elastic+inelastic) cross sections in the 30-500 eV energy range are calculated and reported. A complex optical potential consisting of static, exchange, correlation-polarization plus absorption contributions is used for the description of the electron-molecule interaction. The Schwinger variational iterative method combined with the distorted-wave approximation is applied to calculate the scattering amplitudes. In addition, experimental absolute elastic differential cross sections generated using the relative flow technique are reported in the 100-400 eV range. Comparison between the calculated results and present measured data and also existing experimental and theoretical results is encouraging.

Electronic excitation of H2O by electron impact

Recently we made calculations of differential and integral cross sections for the X1A1 to 3A1(3a1 to 3sa1) transition in H2O in the energy range of 12-30 eV, where the distorted-wave approximation was applied for the first time to study the electronic excitation of a nonlinear polyatomic target by electron impact. In the present work we make an extension of this calculation for that transition to the energy range 40-150 eV. Calculations of cross sections for the X1A1 to 3A1(3a1 to 3pa1) transition in the energy range 14-150 eV are also reported. The present study is the first theoretical investigation of electron-impact excitation of the channel 3a1 to 3pa1 in this nonlinear molecule.

Elastic and excitation cross sections for electron - nitrous oxide collisions

In this work, we present a theoretical study of elastic and inelastic electron - collisions in the low and intermediate incident energy range. More specifically, we report differential and integral cross sections for the elastic scattering in the 5 to 80 eV range as well as the excitation cross sections for the transitions leading to the lowest and states in the 10 to 100 eV range. The Born-closure Schwinger variational method was applied for the elastic scatterings whereas the distorted-wave method was used to study the electron impact excitation processes. The calculations were carried out using the fixed-nuclear static-exchange approximation at the equilibrium geometry of the ground-state . The comparison between the calculated results and the available experimental data in the literature is encouraging. .

Elastic and total cross sections for electron-carbonyl sulfide collisions

In this paper, we report a joint theoretical-experimental study on electron-OCS collisions in the low- and intermediate-energy ranges. More specifically, elastic differential and integral cross sections, as well as grand total (elastic + inelastic) cross sections in the 0.4-600 eV energy range, are reported. A complex optical potential consisting of static, exchange, correlation-polarization plus absorption contributions, derived from a fully molecular wavefunction, is used for the electron-molecule interaction. The Schwinger variational iterative method, combined with the distorted-wave approximation, is applied to calculate the scattering amplitudes. Additionally, we also report measured elastic differential and integral cross sections in the 100-600 eV energy range determined using the relative-flow technique. Comparison between calculated results and present and existing experimental data, as well as with other theoretical results, is encouraging.

Elastic and total cross sections for electron-carbon disulfide collisions

In this work, we report on a theoretical study of electron-CS2 collision in the low- and intermediate-energy range. More specifically, the elastic differential and integral cross sections as well as the grand total (elastic+inelastic) cross sections in the 0.05-100 eV range are reported. A complex optical potential consisting of static, exchange, correlation-polarization plus absorption contributions, derived from a fully molecular wavefunction, is used for the electron-molecule interaction. The Schwinger variational iterative method combined with the distorted-wave approximation are applied to calculate the scattering amplitudes. The comparison between the calculated results and the existing experimental and theoretical results is encouraging.

Elastic and total cross sections for electron scattering by nitrogen molecule in the intermediate energy range

The Schwinger variational iterative method combined with the distorted-wave approximation is applied to the calculation of differential, integral and momentum transfer cross sections for elastic electron- scattering in the 20-800 eV energy range. In this study, a complex optical potential consisting of static, exchange, correlation-polarization plus absorption contributions, derived from a fully molecular wavefunction, is used for the electron-molecule interaction. It is shown that the introduction of absorption effects influences significantly the calculated differential cross sections in the intermediate and high incident energy range. Particularly, in the 50-300 eV range, the used model absorption potential has improved significantly the agreement between calculated results and the available experimental data.

Elastic Cross Sections for Low-Energy e--CH4 Collisions

Recently we have extended our codes based on the Schwinger variational iterative method in order to study elastic electron scattering by non-planar molecules with symmetries reducible to the C2v point group and also to include a correlation- polarization contribution to the electron-molecule interaction potential. In this work we report the first application of these newly extended codes to the calculation of cross sections for low-energy elastic scattering of electron by methane. Differential, integral and momentum-transfer cross sections were calculated in the 0.1-50 eV incident energy range. Comparison of our results with the extensive available data, both experimental and theoretical, reveals the reliability of our method. Particularly, the Ramsauer minimum at around 0.4 eV and the resonance structure at around 8 eV are well reproduced in our calculations.

Application of the method of continued fractions for electron scattering by linear molecules

The method of continued fractions (MCF) of Horacek and Sasakawa (1983) is adapted for the first time to study low-energy electron scattering by linear molecules. Particularly, we have calculated the reactance K-matrices for an electron scattered by hydrogen molecule and hydrogen molecular ion as well as by a polar LiH molecule in the static-exchange level. For all the applications studied herein, the calculated physical quantities converge rapidly, even for a strongly polar molecule such as LiH, to the correct values and in most cases the convergence is monotonic. Our study suggests that the MCF could be an efficient method for studying electron-molecule scattering and also photoionization of molecules.

Photoionization of CF4 in the VUV region

Abstract We present calculated results of photoionization cross sections and photoelectron angular distributions for ionization out of the five outermost valence orbitals of CF 4 for photon energies ranging from near threshold to 55 eV. The Schwinger variational iterative method, using an exact static-exchange plus a model correlation–polarization potential, is applied to obtain the continuum photoelectron orbitals. The quantitative agreement between our calculated results and the experimental data is fair. Moreover, our study is capable of identifying most structures seen in experimental results for both cross sections and asymmetry parameters.