DFT study of low-energy electron interaction with pyridine, pyrazine and their halo derivatives

In this work, the density functional theory with B3LYP hybrid functional was employed to calculate quantities useful for estimating the behavior of pyridine, pyrazine and their derivatives monosubstituted with Cl or Br atom, when exposed to low-energy electron impact. Vertical electron affinities obtained in several Pople basis sets and in aug-cc-pVTZ basis set are reported. Although some of the investigated molecules do not form stable anions, the results are in a satisfactory agreement with the available, albeit sparse experimental data, if the diffuse functions are included in calculations. It was found that the 6-31+G* basis is sufficient and its further enlargement does not significantly change the results. At this level of theory, potential energy curves, supported by enthalpies of dissociation to the neutral and anion fragment, were also determined for the description of the dissociative electron attachment. According to B3LYP, the potential energy curves of the halogen bond are almost repulsive in halopyridines, whereas halopyrazine anions require small activation energy for dissociation. Vertical electron affinities, enthalpies and equilibrium C-X distances (X=H, Cl, Br) were also calculated using Møller-Plesset second-order perturbation theory. Graphic Abstract