Violaine Vizcaino

Absolute elastic cross-sections for low-energy electron scattering from tetrahydrofuran

We present results for elastic electron collision cross-sections with tetrahydrofuran (C4H8O) in the energy range of 6.5–50 eV. The absolute cross-sections are determined from crossed beam measurements using the relative flow technique and cover the angular range between 10° and 130°. Integral and momentum transfer cross-sections have also been derived from these results. The data, where possible, are compared to recent experimental results and theoretical calculations.

Bond dissociation of the dipeptide dialanine and its derivative alanine anhydride induced by low energy electrons

Dissociative electron attachment to dialanine and alanine anhydride has been studied in the gas phase utilizing a double focusing two sector field mass spectrometer. We show that low-energy electrons (i.e., electrons with kinetic energies from near zero up to 13 eV) attach to these molecules and subsequently dissociate to form a number of anionic fragments. Anion efficiency curves are recorded for the most abundant anions by measuring the ion yield as a function of the incident electron energy. The present experiments show that as for single amino acids (M), e.g., glycine, alanine, valine, and proline, the dehydrogenated closed shell anion (M-H)(-) is the most dominant reaction product. The interpretation of the experiments is aided by quantum chemical calculations based on density functional theory, by which the electrostatic potential and molecular orbitals are calculated and the initial electron attachment process prior to dissociation is investigated.

Elastic electron scattering from 3-hydroxytetrahydrofuran: experimental and theoretical studies

We report the results of measurements and calculations for elastic electron scattering from 3-hydroxytetrahydrofuran (C4H8O2). The measurements are performed with a crossed electron-target beam apparatus and the absolute cross-sections are determined using the relative flow technique. The calculations are carried out using the Schwinger multichannel method in the static-exchange plus polarization (SEP) approximation. A set of angular differential cross-sections (DCS) is provided at five incident energies (6.5, 8, 10, 15 and 20 eV) over an angular range of 20–130°, and the energy dependence of the elastic DCS at a scattering angle of 120° is also presented. Integral elastic and elastic momentum transfer cross-sections have also been derived and calculated. The results are compared with those of recent measurements and calculations for the structurally similar molecule tetrahydrofuran (C4H8O).

Elastic electron scattering from formic acid (HCOOH): absolute differential cross-sections

We report experimental results for electron scattering from formic acid (HCOOH). A set of differential cross-sections is provided for elastic scattering at incident electron energies from 1.8 to 50 eV. Integral and momentum transfer cross-sections have also been derived from these results. Our results are compared, where possible, with recent theoretical calculations.

Electron attachment to CO2 embedded in superfluid He droplets.

Electron attachment to CO2 embedded in superfluid He droplets leads to ionic complexes of the form (CO2)n– and (CO2)nO– and, at much lower intensities, He containing ions of the form Hem(CO2)nO–. At low energies (<5 eV), predominantly the non-decomposed complexes (CO2)n– are formed via two resonance contributions, similar to electron attachment to pristine CO2 clusters. The significantly different shapes and relative resonance positions, however, indicate particular quenching and mediation processes in CO2@He. A series of further resonances in the energy range up to 67 eV can be assigned to electronic excitation of He and capture of the inelastically scattered electron generating (CO2)n– and two additional processes where an intermediately formed He* leads to the nonstoichiometric anions (CO2)nO–.

Electron Attachment to CO2 Embedded in Superfluid He Droplets

Electron attachment to CO2 embedded in superfluid He droplets leads to ionic complexes of the form (CO2)n– and (CO2)nO– and, at much lower intensities, He containing ions of the form Hem(CO2)nO–. At low energies (<5 eV), predominantly the non-decomposed complexes (CO2)n– are formed via two resonance contributions, similar to electron attachment to pristine CO2 clusters. The significantly different shapes and relative resonance positions, however, indicate particular quenching and mediation processes in CO2@He. A series of further resonances in the energy range up to 67 eV can be assigned to electronic excitation of He and capture of the inelastically scattered electron generating (CO2)n– and two additional processes where an intermediately formed He* leads to the nonstoichiometric anions (CO2)nO–.

Formation and decay of the dehydrogenated parent anion upon electron attachment to dialanine.

Abstract The dehydrogenated parent anion [M−H]− is one of the most dominant anions formed in dissociative electron attachment to various small biomolecules like nucleobases and single amino acids. In the present study, we investigate the [M−H]− channel for the dipeptide dialanine by utilizing an electron monochromator and a two-sector-field mass spectrometer. At electron energies below 2 eV, the measured high-resolution ion-efficiency curve has a different shape to that for the single amino acid alanine, which is explained by the altered threshold energies for formation of [M−H]− determined in quantum chemical calculations. Moreover, the structure of the formed [M−H]− anion is further studied by investigating the unimolecular and collision-induced decay of this anion. Trajectory calculations have been carried out to aid the interpretation of the experimentally observed fragmentation patterns.

Dissociative Electron Attachment to β‐Alanine

A detailed study on dissociative electron attachment (DEA) to β-alanine (βA) in the gas phase is presented. Ion yields as a function of the incident electron energy from about 0 to 15 eV have been measured for most of the fragments. As for all α-amino acids, the main reaction corresponds to the loss of a hydrogen atom, although many other fragments have been observed that involved more complex bond cleavages. Threshold energies have been calculated by using the G4(MP2) method for various decomposition reactions. Fragmentation pathways were also investigated to measure metastable decays of the intermediate fragment anion (βA-H)(-) by using the mass-analyzed ion kinetic energy (MIKE) scan technique. Comparisons with α-alanine and other amino acids are made when relevant.

Low energy (0–4 eV) electron impact to N2O clusters: Dissociative electron attachment, ion-molecule reactions, and vibrational Feshbach resonances

Electron attachment to clusters of N(2)O in the energy range of 0-4 eV yields the ionic complexes [(N(2)O)(n)O](-), [(N(2)O)(n)NO](-), and (N(2)O)(n) (-) . The shape of the ion yields of the three homologous series differs substantially reflecting the different formation mechanisms. While the generation of [(N(2)O)(n)O](-) can be assigned to dissociative electron attachment (DEA) of an individual N(2)O molecule in the target cluster, the formation of [(N(2)O)(n)NO](-) is interpreted via a sequence of ion molecule reactions involving the formation of O(-) via DEA in the first step. The nondecomposed complexes (N(2)O)(n) (-) are preferentially formed at very low energies (below 0.5 eV) as a result of intramolecular stabilization of a diffuse molecular anion at low energy. The ion yields of [(N(2)O)(n)O](-) and (N(2)O)(n) (-) versus electron energy show sharp peaks at the threshold region, which can be assigned to vibrational Feshbach resonances mediated by the diffuse anion state as already observed in an ultrahigh resolution electron attachment study of N(2)O clusters [E. Leber, S. Barsotti, J. Bömmels, J. M. Weber, I. I. Fabrikant, M.-W. Ruf, and H. Hotop, Chem. Phys. Lett. 325, 345 (2000)].

Very Low Energy Electrons Transform the Cyclobutane‐Pyrimidine Dimer into a Highly Reactive Intermediate

Electrons with virtually no kinetic energy (close to 0 eV) trigger the decomposition of cytotoxic cyclobutane-pyrimidine dimer (CPD) into a surprisingly large variety of fragment ions plus their neutral counterparts. The response of CPD to low energy electrons is thus comparable to that of explosives like trinitrotoluene (TNT). The dominant unimolecular reaction is the splitting into two thymine like units, which can be considered as the essential molecular step in the photolyase of CPD. We find that CPD is significantly more sensitive towards low energy electrons than its thymine building blocks. It is proposed that electron attachment at very low energy proceeds via dipole bound states, supported by the large dipole moment of the molecule (6.2 D). These states act as effective doorways to dissociative electron attachment (DEA).