Low-energy electron collisions with glycine

Abstract

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.

The electron-furfural scattering dynamics for 63 energetically open electronic states

“…In the present study, we also employed the Schwinger multichannel method with pseudopotentials (SMCPP) [40][41][42] to obtain theoretical cross sections for the excitation of the previously discussed bands 4 of furfural by electron impact. This theory was recently reviewed in Ref.…”

Shape resonance spectra of lignin subunits

“…Though a broad and low-lying resonance with σ * OH character would in principle be expected, we found no clear signature of such a state. As discussed elsewhere [21], this assignment would be difficult in view of the s-wave contribution, the large background, and even the coupling to virtual or dipole-supported states. Inspection of the lowest unoccupied molecular orbitals (LUMOs) obtained with the compact 6-31G(d) basis set, a procedure routinely employed in ETS assignments [29], suggests that a σ * OH resonance would indeed exist (this is also supported by DEA data [28]).…”

“…This variational approach to the T -matrix was discussed in detail elsewhere [21,22] and relies on a discrete trial set to expand the scattering state. The present calculations were performed in two approximations, namely, static-exchange (SE) and static-exchange plus polarization (SEP).…”

“…Integral cross sections (ICSs) were obtained with the parallel version [21] of the Schwinger multichannel method with pseudopotentials (SMCPP) [22]. This variational approach to the T -matrix was discussed in detail elsewhere [21,22] and relies on a discrete trial set to expand the scattering state.…”

Theory of dissociative electron attachment: Biomolecules and clusters

“…In spite of the DR2013 success of this approach, particularly in description of VFRs, and in spite of the excellent agreement with experiments on formic acid [27], several objections were made with regard to the existence of the * resonance in these systems. Indeed the standard Breit-Wigner parametrization of the scattering eigenphases did not allow for detection of a low-energy * resonance in formic acid [28], uracil [29][30][31] or glycine [32]. Our studies [19,25] showed that the * resonances in these systems at the equilibrium nuclear geometry are extremely broad with the resonance width reaching 5-6 eV, therefore the resonance width actually exceeds the resonance energy.…”