Figure 1

Present integral elastic cross sections for positron scattering by pyrimidine computed with: (a) the $R$-matrix method at the SP level using the cc-pVDZ basis set (dashed-dotted blue line) and the diffuse basis set 6-311+G${}^{**}$ (dashed light-green line), and at the CC level (cc-pVDZ) (solid dark-green line). Both uncorrected (thin lines) and Born-corrected (thick lines) cross sections are given. This quantum scattering method is expected to be valid up to the Ps formation threshold, which is indicated by a black-dotted line. (b) The IAM-SCAR method with the dipole polarization potential [solid black thin line (•)] and dipole plus quadrupole polarization potential [solid blue thin line (×)], also uncorrected (thin lines) and including the Born dipole allowed rotational excitations (thick lines). The region of validity of this method, namely for energies above about 30 eV, is also indicated by a black-dotted line, which is placed at 30 eV (see text for details).Reuse & Permissions

Figure 2

The present computed integral elastic cross sections for positron scattering by pyrimidine computed with the $R$-matrix method (at the SP and CC levels of approximation) and with the IAM-SCAR method (using $V_d$ and $V_d$${}_{+p}$), with and without Born-type correction (same legend as in Fig. 1). Additionally we have plotted, for comparison, the electron scattering elastic integral cross sections with (dotted red thick line) and without (dotted red thin line) the Born correction, as obtained by combining the $R$-matrix [25] and IAM-SCAR methods as shown in Sanz et al. [27].Reuse & Permissions

Figure 3

Elastic differential cross sections for positron scattering from pyrimidine, for the incident energies indicated in the panels. Results from the $R$-matrix approach at SP level using the cc-pVDZ (dashed-dotted blue line) basis and the diffuse basis set 6-311+G${}^{**}$ (dashed light-green line), and at the CC level with the compact basis set (solid dark-green line) are shown. Also plotted are the IAM-SCAR results with dipole polarization potential [solid black line (•)] and dipole plus quadrupole polarization potential [solid blue line (×)]. All the $R$-matrix results are Born corrected and all the IAM-SCAR results are Dickinson corrected. For comparison we show the improved computed electron elastic DCS shown in Sanz et al. [27], as calculated with the $R$-matrix approach up to the ionization potential and then with IAM-SCAR method for higher energies.Reuse & Permissions

Figure 4

The present computed total cross sections for positron scattering by pyrimidine: $R$-matrix results at the CC level using the cc-pVDZ basis set (solid dark-green thin-line), IAM-SCAR results with dipole polarization potential [solid black thin line (•)] and dipole plus quadrupole polarization potential [solid blue thin line (×)]. Also plotted are the TCS including the Born dipole-induced rotational excitations: $R$-matrix results at the CC level using the cc-pVDZ basis set (solid dark-green thick line), IAM-SCAR results with dipole polarization potential [solid black thick line (•)] and dipole plus polarization potential [solid blue thick line (×)]. These results are compared with the experimental data of Zecca et al. [24]. For comparison the computed electron total cross sections with (dotted red thick line) and without (dotted red thin line) Born correction, shown in Sanz et al. [27] are also plotted. In addition, the present inelastic integral cross sections computed with the $R$-Matrix approach (dashed-dotted blue thick line) and the IAM-SCAR (dashed-dotted blue thin line) method are given.Reuse & Permissions