We have investigated the effect of microsolvation on the π* shape resonances of uracil, referred to as π1* and π2* in the order of increasing energy. Our study considered uracil–water aggregates with six solvent molecules obtained from Monte Carlo simulations in the liquid phase. To explore the ensemble statistics, we combined scattering calculations, performed in the static exchange and static exchange plus polarization approximations, with linear regressions of virtual orbital energies to the scattering results. In general, the solvent molecules stabilize the anion states, and the lower lying π1* resonance becomes a bound state in most of the solute–water clusters. We also discuss how the strength of the H bonds can affect the energies of the anion states, in addition to the number and donor/acceptor characters of those bonds. The thermal distributions for the vertical attachment energies, obtained from 133 statistically uncorrelated solute–solvent clusters, are significantly broad in the energy scale of the autoionization widths. The distributions for the π1* and π2* anion states slightly overlap, thus giving rise to a quasi-continuum of attachment energies below ≲2.5 eV, in contrast to the gas phase picture of electron attachment to well separated resonances below the electronic excitation threshold. Both the stabilization of the anion states and the spread of attachment energies could be expected to favor the dissociative electron attachment processes believed to underlie the electron-induced damage to biomolecules.

In the search for alternatives to chlorine-containing gases, tetrafluoroethane, CF3CH2F (R134a), a widely used refrigerant gas, has been recognized as a promising substitute for dichlorodifluoromethane, CCl2F2 (R12). When R12 is replaced by R134a, the global warming potential drops from 8100 to 1430, the ozone depletion potential changes from 1 to 0, and the atmospheric lifetime decreases from 100 to 14 years. Electron interactions in the gas phase play a fundamental role in the atmospheric sciences. Here, we present a detailed study on electron-driven fragmentation pathways of CF3CH2F, in which we have investigated processes induced by both electron ionization and electron attachment. The measurements allow us to report the ion efficiency curves for ion formation in the energy range of 0 up to 25 eV. For positive ion formation, R134a dissociates into a wide assortment of ions, in which CF3 + is observed as the most abundant out of seven ions with a relative intensity above 2%. The results are supported by quantum chemical calculations based on bound state techniques, electron-impact ionization models, and electron-molecule scattering simulations, showing a good agreement. Moreover, the experimental first ionization potential was found at 13.10 ± 0.17 eV and the second at around 14.25 eV. For negative ion formation, C2F3 – was detected as the only anion formed, above 8.3 eV. This study demonstrates the role of electrons in the dissociation of R134a, which is relevant for an improvement of the refrigeration processes as well as in atmospheric chemistry and plasma sciences.

In the present study, we investigated the formation of negative ions following electron attachment to benzaldehyde in the gas-phase.

We report on the low energy anion spectra of 5-cyanateuracil (5-OCNU) and 5-thiocyanateouracil (5-SCNU), which have been the suggested potential radiosensitizers for use in cancer therapy [L. Chomicz et al., J. Phys. Chem. Lett. 4, 2853-2857 (2013)]. Employing bound state and scattering calculations, we obtained, for both molecules, a dipole bound state, a π valence bound state, and four π resonances, besides a σ resonance for 5-SCNU. The cyanate and thiocyanate substituents give rise to additional long-lived π resonances, compared to 5-halouracil radiosensitizers. From the reaction thresholds and the expected vibronic couplings among the anion states, efficient production of SCN and CN anions and radical fragments should be observed in dissociative electron attachment measurements for 5-SCNU. The corresponding dissociation processes in 5-OCNU are expected to be less effective in view of the lack of a long-lived σ shape resonance and the little σ admixture into the π resonances located on the cyanate group. The present results thus indicate 5-SCNU as a more promising radiosensitizer at sub-excitation energies.