We report cross sections for elastic electron scattering by gas phase glycine (neutral form), obtained with the Schwinger multichannel method. The present results are the first obtained with a new implementation that combines parallelization with OpenMP directives and pseudopotentials. The position of the well known π* shape resonance ranged from 2.3 eV to 2.8 eV depending on the polarization model and conformer. For the most stable isomer, the present result (2.4 eV) is in fair agreement with electron transmission spectroscopy assignments (1.93 ± 0.05 eV) and available calculations. Our results also point out a shape resonance around 9.5 eV in the A' symmetry that would be weakly coupled to vibrations of the hydroxyl group. Since electron attachment to a broad and lower lying σ* orbital located on the OH bond has been suggested the underlying mechanism leading to dissociative electron attachment at low energies, we sought for a shape resonance around ~4 eV. Though we obtained cross sections with the target molecule at the equilibrium geometry and with stretched OH bond lengths, least-squares fits to the calculated eigenphase sums did not point out signatures of this anion state (though, in principle, it could be hidden in the large background). The low energy (~1 eV) integral cross section strongly scales as the bond length is stretched, and this could indicate a virtual state pole, since dipole supported bound states are not expected at the geometries addressed here.

We report elastic integral cross sections for low-energy electron scattering by gas-phase dimethyl sulfide and dimethyl disulfide, obtained with the Schwinger multichannel method with pseudopotentials. Our symmetryresolved cross sections for dimethyl sulfide reveal that the single broad structure at 3.25 eV observed in the electron transmission spectrum (assigned as a σ * CS shape resonance) would actually arise from two superimposed anion states in the B 2 and A 1 symmetry components of the C 2v point group. We also obtained two low-lying shape resonances for dimethyl disulfide, in good agreement with the available electron transmission data. In view of the recently reported measurements on dissociative electron attachment to dimethyl disulfide [C. Matias, A. Mauracher, P. Scheier, P. Limão-Vieira, and S. Denifl, Chem. Phys. Lett. 605-606, 71 (2014)], we also calculated cross sections for stretched S-S bond lengths, which indicate a fast stabilization consistent with the experimental data.

Abstract. We report on recent advances in studies of transient ions formed in electron and positron scattering by molecules. We briefly discuss elastic electron collisions against pyrrole and glycine, as well as electron affinities of glycine-water clusters. Positron scattering and annihilation on small molecules is also discussed.

Synopsis We report on recent advances in studies of transient ions formed in electron scattering by molecules. We briefly discuss elastic electron collisions against glycine, as well as electron affinities of glycine-water clusters.Considerable attention has been devoted u to electron interactions with biomolecules since the discovery of mutagenic rupture of DNA strands through a dissociative electron attachment (DEA) mechanism [1,2]. In this process, the electrons are trapped in resonance states localized on subunits of the biomolecules, where these transient anion states usually have either a (σ) or (π * ) character.Amino-acids are constituents of proteins and these can undergo dissociative electron attachment (DEA). Different amino-acids are expected to selectively capture electrons taking into account the variety of structure, with recent discussion on the DEA mechanism prevailing in carboxyl groups [3,4]. We report on recent advances in studies of transient ions formed in electron scattering by glycine amino-acids. Our scattering studies performed with the Schwinger Multichannel Method with Pseudopotentials (SM-CPP) [5] indicate the existence of one (π * ) resonance strongly localized on C = O and two (σ * ) resonance localized on O − H.We also report on electron interactions with glycine-water clusters. The fact that biologically relevant systems exist in solution is a clear limitation of gas-phase studies of biomolecules, and this drawback is particularly evident for aminoacids since the neutral form is more stable in the gas phase while the zwitterionic form is more stable in solution. To explore dissociative effects we performed SMCPP studies of electron scattering by neutral glycine and electron affinity studies of glycine-water clusters in both forms, employing two well-established methodology [6] based on density functional theory.