We report elastic integral and differential cross sections for positron collisions with pyrazine (C4H4N2), for energies up to 10 eV. The cross sections were calculated with the Schwinger multichannel method in the static plus polarization approximation. Our computed elastic integral cross section indicates the presence of a Ramsauer–Townsend minimum and a bound state in the A g scattering symmetry. In the absence of results in the literature on collisions of positrons with pyrazine, we compare the present results with results for pyrimidine and benzene molecules available in the literature.

No abstract

No abstract

The Schwinger multichannel method is employed to study elastic and electronically inelastic collisions of low-energy electrons by the thiophene molecule. It is well known that the elastic integral cross section for electron-thiophene scattering presents three shape resonances, some of which located around the opening region of the first excited state. The main purpose of this work is to evaluate the influence of polarization effects on the positions of the resonances appearing in the elastic channel and its potential impact on the description of the electronic excitation process involving the transition from ground state to the 3B2 excited state of thiophene. Our cross section results indicate that target polarization may affect the electronic excitation process in the region of the threshold of the 3B2 excited state, but its impact seems to be related to the effect of polarization on the resonances in the elastic channel. More specifically, there are cases (A2 and B1 symmetries) where the overlap of the shape resonance with the threshold changes significantly with the inclusion of polarization resulting in a considerable modification in the magnitude of the electronically inelastic cross section, while in other case (B2 symmetry) a similar overlap is not accompanied by sensible changes in the magnitude of the excitation cross section. Our excitation functions at scattering angles of 90° and 135° are compared with the calculations and measurements of Loupas et al (2018 J. Phys. Chem. A 122 1146) and show in general a qualitative agreement.

We report elastic, electronically inelastic, total ionization and total cross sections for the scattering of electrons by trans-formic acid. The calculations of the elastic and electronically inelastic cross sections were performed with the Schwinger multichannel method implemented with norm-conserving pseudopotentials. The electronically inelastic calculations were done within the minimal orbital basis for single configuration interaction approach with different multichannel coupling schemes considering from 1 up to 51 open channels, which enable us to study the influence of the multichannel coupling effects on the calculated cross sections. Polarization effects in the elastic channel were taken into account considering only the excitations related to the pairs used in the minimal orbital basis for single configuration interaction approach. We found that the magnitude of the elastic and inelastic cross sections decreases as more channels are treated as open in the scattering calculations. The calculated elastic differential cross sections present an overall good agreement with previous studies found in the literature. The elastic integral cross section presents a well-known π * shape resonance centered at 1.96 eV. The total ionization cross section was calculated with the binary-encounter-Bethe model and presents a good agreement with previous results from the literature. The total cross section was estimated using the calculated elastic, inelastic and ionization cross sections.