Search

We report the results of a study on electron-target correlations in the 2Πg shape resonance of elastic e-N2 scattering, using the Schwinger multichannel formulation. The effects of basis set, orbital representation, and closed-channel configurations are delineated. The different roles of radial and angular correlations are compared. Our results are in good agreement with a recent calculation by Schneider and Collins [Phys. Rev. A 30, 95 (1984)] using the linear algebraic-optical potential method whereas calculations using radial correlations alone agree well with previous calculations based on a variety of different approaches.

In this paper we report cross sections for electron-impact excitation of the X 1Σg+→B 1Σu+ transition in H2 for collision energies of 15, 20, and 30 eV. For this dipole-allowed transition with its associated long-range potential, the contributions of the more strongly scattered low-angular-momentum partial waves to the cross section were obtained from a two-state Schwinger multichannel calculation, and a modified Born-closure scheme was used to include the contributions from the remaining weakly scattered partial waves. Agreement between the calculated differential cross sections and available experimental data is encouraging.

The rotational branching ratios resulting from (1+1) resonant-enhanced multiphoton ionization of NO via the A 2Σ+ Rydberg state are analyzed. Theoretical results using ab initio molecular parameters agree reasonably well with recent experimental data. More importantly, the analysis underscores the importance of the molecular nature of the problem and its resulting complexities. It is shown that, for photoionization of a Σ state that leaves the ion in a Σ state, the allowed rotational states of the ion satisfy the selection rule ΔN+l=odd, where ΔN is the difference in (electronic + rotational) quantum numbers for the neutral and for the ion, and l is the partial wave of the electron. Based on this selection rule, it follows that the predominantly gerade 3sσ Rydberg orbital of the A 2Σ+ state couples only to the ungerade channel in the continuum (l odd), thereby suppressing the ΔN=±1 peaks, in agreement with experiment. The molecular nature of the ionic potential leads to strong l mixing in electronic continuum orbitals. In fact, the influence of a nearby shape resonance causes the f wave to be dominant in the σ channel.

We report inelastic differential cross sections for electronic excitation of an oriented molecule by low-energy electrons. Specifically we look at the dependence of these cross sections for the X1Σg+→b3Σu+ transition in H2 on both incident and scattered angles as well as on impact energy. These electron scattering cross sections exhibit a pronounced dependence on the incident and scattered angles, which suggests that related electron-energy-loss spectroscopy studies can be a useful probe of adsorbate-substrate structure.

We report elastic differential and momentum transfer cross sections for the elastic scattering of electrons by H2O for collision energies from 2 to 20 eV. These fixed-nuclei static-exchange cross sections were obtained using the Schwinger variational approach. In these studies the exchange potential is directly evaluated and not approximated by local models. The calculated differential cross sections, obtained with a basis set expansion of the scattering wave function, agree well with available experimental data at intermediate and larger angles. As used here, the results cannot adequately describe the divergent cross sections at small angles. An interesting feature of the calculated cross sections, particularly at 15 and 20 eV, is their significant backward peaking. This peaking occurs in the experimentally inaccessible region beyond a scattering angle of 120°. The implication of this feature for the determination of momentum transfer cross sections is described.

The Schwinger multichannel formulation has been applied to study the role of electron correlation in low-energy e-N2 scattering. For the five nonresonant partial-wave channels studied here, 2Σg+, 2Σu+, 2Πu, 2Δg, and 2Δu, we find angular correlation to be much more important than radial correlation. Our results for the 2Σg+ channel are in agreement with those of Schneider and Collins [Phys. Rev. A 30, 95 (1984)]. Our calculated total and differential cross sections agree with experiment except for the differential cross sections at 1.5 eV. Our results are also compared with those obtained using model polarization potentials.

We report the first application of the Schwinger multichannel formulation to low-energy electron collisions with a nonlinear polyatomic target. Integral and differential cross sections are obtained for e-CH4 collisions from 3 to 20 eV at the static-plus-exchange interaction level. In these studies the exchange potential is directly evaluated and not approximated by local models. An interesting feature of the small-angle differential cross section is ascribed to polarization effects and not reproduced at the static-plus-exchange level. Our differential cross sections are found to be in reasonable agreement with existing measurements at 7.5 eV and higher energies.