We report computed cross sections for the elastic scattering of slow electrons by the pyrimidine bases of DNA, thymine and cytosine, and by the associated nucleosides, deoxythymidine and deoxycytidine. For the isolated bases, we carried out calculations both with and without the inclusion of polarization effects. For the nucleosides, we neglect polarization effects but estimate their influence on resonance positions by comparison with the results for the corresponding bases. Where possible, we compare our results with experiment and previous calculations.

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We report cross sections for low-energy elastic electron scattering by pyrrole, obtained with the Schwinger multichannel method implemented with pseudopotentials. Our calculations indicate pi( *) shape resonances in the B(1) and A(2) symmetries, and two sigma( *) resonances in the A(1) symmetry (the system belongs to the C(2v) point group). The present assignments of pi( *) resonances are very close to those previously reported for the isoelectronic furan molecule, in agreement with electron transmission spectra. The lowest-lying sigma( *) anion is localized on the N-H bond and provides a dissociation coordinate similar to those found in the hydroxyl groups of organic acids and alcohols. This sigma(NH) ( *) resonance overlaps the higher-lying pi( *) resonance (possibly both pi( *) states) and could give rise to direct and indirect dissociation pathways, which arise from electron attachment to sigma( *) and pi( *) orbitals, respectively. The photochemistry of pyrrole and 9-H adenine is similar, in particular with respect to the photostability mechanism that allows for the dissipation of the photon energy, and we believe pyrrole would also be a suitable prototype for studies of dissociative electron attachment (DEA) to DNA bases. We point out the connection between the mechanisms of photostability and DEA since both arise from the occupation of sigma( *) and pi( *) orbitals in neutral excited states and in anion states, respectively.

We report on a combination of experimental and theoretical investigations into the elastic differential cross sections (DCS) and integral cross sections (ICS) for electron interactions with dichloromethane, CH 2 Cl 2 , in the incident electron energy over the 7.0-30 eV range. Elastic electron scattering cross section calculations have been performed within the framework of the Schwinger multichannel method implemented with pseudopotentials (SMCPP), and the independent atom model with screening corrected additivity rule including interference effects correction (IAM-SCAR+I). The present elastic DCSs have been found to agree reasonably well with the results of IAM-SCAR+I calculations above 20 eV, and also with the SMC calculations below 30 eV. Although some discrepancies were found for 7 eV, the agreement between the two theoretical methodologies is remarkable as the electron impact energy increases. Calculated elastic DCSs are also reported up to 1000 eV for scattering angles from 0º to 180º together with total cross section (TCS) within the IAM-SCAR+I framework.

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