R-matrix calculation of Rydberg states of CO

Abstract

Valence and Rydberg bound states of CO are studied ab initio using the UK molecular R-matrix code and electron-CO + scattering calculations. Results are presented for singlet and triplet + and states of CO at R = 2.132 a 0 . Various models for both the CO + target and the full calculation are tested and the stability of the final models is demonstrated. Final calculations employ complete active space (CAS) target states, with and without further excitation, and up to 13 target states in the close-coupling expansion. The best model underestimates the ionization potential of CO by 0.1 eV and finds quantum defects systematically slightly higher than those observed, by up to 0.07. The prospects for further improvement of these calculations are discussed.

Elastic and inelastic low-energy electron collisions with pyrazine

“…In our calculations, we choose to base our target models around the complete active space (CAS) CI representation of the target wavefunction. This model has been found to produce a satisfactorily balanced results for small targets 41 when a simple set of L 2 functions suffices. Here, we need to expand this model in order to achieve a good description of the resonances and balance is therefore harder to achieve.…”

Uncertainty estimates for theoretical atomic and molecular data

“…We note that Rydberg states form regular series, which are often well represented by quantum defect theory [80]. Experience shows that uncertainties in these states can also often be better represented in terms of quantum defects rather than absolute energies [81,82], although other methods can be used for calculations including assessment of uncertainties [83].…”

Low-energy electron scattering with the purine bases of DNA/RNA using the R-matrix method

“…To obtain the L 2 configurations for the CC model, the extra electron is added to this set of active electrons; this ensures a good balance of electron-electron correlation between the target and the scattering calculation in the CC model. A standard CC calculation involves contraction of configurations arising from placing the scattering electron into the virtual and scattering orbitals, 32 i.e., including the virtual orbitals as part of the first sum in Eq. (1).…”