No abstract

We report computed differential cross sections (DCSs) for electron impact excitation of the lower-lying states of both trans and gauche tautomers of ethanol, as well as total cross sections for the 15 eV–50 eV energy range. The Schwinger multichannel (SMC) method with pseudopotentials has been employed, and in our most sophisticated calculation in terms of multichannel coupling, 431 open target states have been considered. We found an overall good agreement with the available experimental data at intermediate scattering angles and at higher impact energies. Although we have used a Born-closure scheme for the higher partial waves, we have found discrepancies in the forward direction that were assigned to a poor description of the long-range component of the lower partial waves. Meanwhile, the lack of more Rydberg states could be related to the overestimated DCSs at lower energies. Missing open channels are usually evoked to explain the remaining discrepancies to experiment, but here, we argue that other factors should also be involved. Aiming at an improved description of the target states, we have proposed a simple procedure for selecting the pairs of hole and particle orbitals while keeping the single excitation prescription of the current SMC implementation. A quantitative assessment of the collision process should further consider the individual contribution of each tautomer, which presented quite distinct DCSs in some cases. Our computed excitation energies also support that the second absorption band of ethanol is comprised of three singlet states of each tautomer, rather than the previously suggested two or four states.

We present experimental and theoretical differential cross sections for elastic electron scattering from benzene. The present experimental results are obtained at incident electron energies ranging from 1 eV to 50 eV and for scattering angles from 10 • to 130 • . The experimental measurements are compared to available results from 1 eV to 10 eV, and to new theoretical results from 10 eV to 50 eV, both based on the Schwinger multichannel (SMC) method. Different electron scattering calculations were carried out, by employing varying basis sets and multichannel coupling schemes. This allowed us to (i) obtain relatively converged cross sections with respect to the inclusion of Rydberg excited states, (ii) observe significant variations in the forward scattering as a function of the multichannel coupling scheme, and (iii) explore possible effects stemming from states lying above the ionization threshold. Overall, the agreement between experiments and models is found to be very good to excellent. The remaining discrepancies point out directions in which the SMC method should be improved.

We propose a model potential for computing total ionization cross sections for atoms and molecules by electron impact. The potential is obtained by a fitting procedure using the Binary-Encounter-Bethe model cross sections as a starting point. We present total ionization cross section for hydrogen, carbon, nitrogen and oxygen atoms and for hydrogen, nitrogen, water, methane and benzene molecules. The results obtained with our model potential are compared with results obtained with the Binary-Encounter-Bethe model and with the first Born approximation, and agreement is quite good. Our results show that this potential could be used to account for the ionization channel in an electron-molecule collision calculation.