Low-energy elastic electron interactions with pyrimidine

We present results of measurements and calculations of elastic electron scattering from pyrimidine in the energy range 3–50 eV. Absolute differential and integral elastic cross sections have been measured using a crossed electron-molecule beam spectrometer and the relative flow technique. The measured cross sections are compared with results of calculations using the well-known Schwinger variational technique and an independent-atom model. Agreement between the measured differential cross sections and the results of the Schwinger calculations is good at lower energies but less satisfactory at higher energies where inelastic channels that should be open are kept closed in the calculations.

Figure 1

Schematic diagram showing the structure of the pyrimidine molecule and pyrimidine nucleobases [9].

Figure 2

Absolute DCS (10${}^{-16}$ cm${}^2$ sr${}^{-1}$) for elastic electron scattering from pyrimidine at (a) 3 eV, (b) 6 eV, (c) 10 eV, (d) 15 eV, (e) 20 eV, and (f) 50 eV. The present measurements are shown as full circles, while previous measurements [9] are shown as triangles in (f). The present theoretical DCS calculated using the SMC method are shown as a solid curve, and the IAM-SCAR calculations are shown as a dashed curve.

Figure 3

Present experimental and theoretical ICS (10${}^{-16}$ cm${}^2$). The experimental cross sections are shown as full circles, the SMC results as a solid curve, and the IAM-SCAR results as a dashed curve.

Figure 4

Symmetry components of the integral elastic cross section for electron scattering by pyrimidine as obtained from the present SMC calculations. The curves are labeled according to the representations of the $C_{2v}$ point group, and the peaks corresponding to three π${}^{*}$ resonances are also indicated.

Figure 5

Absolute DCS (10${}^{-16}$ cm${}^2$ sr${}^{-1}$) shown as a function of energy (EEF) for the energy range of 3–15 eV at scattering angles of (a) 90° and (b) 120°. Also shown are the angular DCS measurements taken at discrete energies in the range of interest.