Elastic and inelastic low-energy electron collisions with pyrazine

Abstract

We present results of ab-initio scattering calculations for electron collisions with pyrazine using the R-matrix method, carried out at various levels of approximation. We confirm the existing experimental and theoretical understanding of the three well-known π * shape resonances. In addition, we find numerous core-excited resonances (above 4.8 eV) and identify their most likely parent states. We also present differential cross sections, showing high sensitivity to the scattering model chosen at low energies. We make recommendations regarding the selection of models for scattering calculations with this type of targets.

Elastic and inelastic cross sections for low-energy electron collisions with pyrimidine

“…The SEP model allows us to better represent short range polarization and correlation effects: changing the number of orbitals included in our virtual space allows us to tune these effects. 46 This model is therefore better at providing positions for the low-lying shape resonances in good agreement with experiment, as well as describing a TABLE II. Vertical excitation energies, calculated at SA-CASSCF level with the indicated basis sets, for the excited electronic states of pyrimidine included in the CC calculation.…”

“…It has a dipole moment 43 2 . Its isomer pyrazine (where the nitrogen atoms are in positions 1 and 4 rather than 1 and 3) has been studied in some detail by us: 46 the calculations presented here are based on the experience gained in that work.…”

“…48 Again, the averaging scheme was selected following tests performed for pyrazine. 46 In our SA-CASSCF calculations, we chose the active space (10,8). This active space comprises 10 electrons distributed among the 6 valence π orbitals and the two lone-pair σ orbitals located on the two nitrogen atoms.…”

An investigation into electron scattering from pyrazine at intermediate and high energies

“…As is appreciated in Fig. 3, the level of accord between the experimental TCS and the IAM-SCAR CS for σ -σ forw markedly improves in the lower energy region and became excellent 20 For comparison, the pyrimidine total CS, both theoretical (dashed-dotted black line; see Sanz et al 48 ) and experimental 22 (purple asterisks) are additionally plotted.…”

“…20 Total cross sections are of significant general importance in scattering investigations 6,7 and are a crucial input for particle track simulations in matter, since in the latter case they are used to calculate the mean-free path between two interactions. Additionally, they serve as an essential reference value for representing the sum of all the partial, process specific, interaction integral cross sections which are typically obtained in independent measurements.…”