Electron scattering in HCl: An improved nonlocal resonance model

We present an improved nonlocal resonance model for electron-HCl collisions. The short-range part of the model is fitted to ab initio electron-scattering eigenphase sums calculated using the Schwinger multichannel method, while the long-range part is based on the ab initio potential-energy curve of the bound anion HCl${}^{-}$. This model significantly improves the agreement of nonlocal resonance calculations with recent absolute experimental data on dissociative electron attachment cross sections for HCl and DCl. It also partly resolves an inconsistency in the temperature effect in dissociative electron attachment to HCl present in the literature. Finally, the present model reproduces all qualitative structures observed previously in elastic scattering and vibrational-excitation cross sections.

Figure 1

Construction of the discrete-state potential $V_d(R)$. Full circles: data from fitting ab initio eigenphase sums; empty circles: data derived from potential-energy curve of Åstrand and Karlström [39]; solid line: final form of $V_d(R)$ as used in the present model.

Figure 2

Eigenphase sums for fixed-nuclei electron-HCl scattering. Dots: Schwinger Multichannel method; solid lines: generalized Breit-Wigner formula (2) with the final parameters of the present nonlocal resonance model. Internuclear distances are $R$ $=$ 2.0, 2.1, 2.2, 2.3, 2.419, 2.5, and 2.6 a.u. (from bottom to top).

Figure 3

Potential-energy functions relevant in the nonlocal resonance model. Dotted line: ground state of neutral HCl, $V_0(R)$; full lines: discrete-state potential $V_d(R)$ and ion potential $V_i(R)$ of the present model; dashed lines: $V_d(R)$ and $V_i(R)$ of the DMHC model [21]; full circles: ab initio HCl${}^{-}$ potential of Åstrand and Karlström.

Figure 4

Dissociative electron attachment to HCl at different temperatures of the neutral target. Dots: experimental data of Allan and Wong [8]; full lines: results of the present model; dashed lines: results of the DMHC model. Theoretical curves were convoluted with a Gaussian of 100 meV FWHM. The experimental data were shifted to higher energies by 35 meV. The vertical scales were normalized so that the curves coincide at the maximum of the 0.88 eV peak.

Figure 5

Vibrational-excitation cross sections. Dots: experimental data of Schafer and Allan [5]; full lines: results of the present model; dashed lines: results of the DMHC model. Theoretical curves were convoluted with a Gaussian of 35 meV FWHM. The experimental data were scaled so that they agree with the present model for the $0\to 2$ cross section near 1 eV.

Figure 6

Relative elastic cross sections (left panel) and relative $0\to 1$ vibrational-excitation cross sections (right panel) in the energy range where oscillatory structures are found. Experimental data are from Ref [6].