Higher lying resonances in low-energy electron scattering with carbon monoxide

TL;DR

This study uses advanced R-matrix calculations to identify higher-lying electron scattering resonances in CO, revealing a narrow Feshbach resonance near the target excitation threshold, with implications for dissociative electron attachment.

Contribution

The paper reports the first identification of a narrow Feshbach resonance in low-energy electron-CO scattering above 1.6 eV using extensive basis set and scattering model tests.

Findings

Discovery of a narrow $^2\Sigma^+$ Feshbach resonance near 12.9 eV

Resonance observed with cc-pVTZ basis set but not with cc-pVDZ

Quantitative cross sections for total, elastic, and electronic excitation

Abstract

R-matrix calculations on electron collisions with CO are reported whose aim is to identify any higher-lying resonances above the well-reported and lowest $^2\Pi$ resonance at about 1.6~eV. Extensive tests with respect to basis sets, target models and scattering models are performed. The final results are reported for the larger cc-pVTZ basis set using a 50 state close-coupling (CC) calculation. The Breit-Wigner eigenphase sum and the time-delay methods are used to detect and fit any resonances. Both these methods find a very narrow $^2\Sigma^+$ symmetry Feshbach-type resonance very close to the target excitation threshold of the b $^3\Sigma^+$ state which lies at 12.9 eV in the calculations. This resonance is seen in the CC calculation using cc-pVTZ basis set while a CC calculation using the cc-pVDZ basis set does not produce this feature. The electronic structure of CO$^-$ is analysed in the asymptotic region, 45 molecular states are found to correlate with states dissociating to an anion and an atom. Electronic structure calculations are used to study the behaviour of these states at large internuclear separation. Quantitative results for the total, elastic and electronic excitation cross sections are also presented. The significance of these results for models of the observed dissociative electron attachment of CO in the 10 eV region is discussed.