eng
Hoffmann, T. H.
Allan, Michael
Franz, K.
Ruf, M.-W.
Hotop, Hartmut
Sauter, G.
Meyer, W.
Resonance structure in electron–N₂ scattering around 11.5 eV: high-resolution measurements, <i>ab initio</i> calculations and line shape analyses
http://doc.rero.ch/record/12946/files/allan_rse.pdf
Using two different experimental setups with energy widths of about 6 and 13 meV, we obtained significantly improved results for the energy dependence of angle-differential (10°–180°) elastic and vibrationally inelastic cross sections for electron scattering from N₂ molecules in the energy range around the narrow N⁻₂(R²Σ⁺<sub>g</sub>) resonance. The energy location and the natural width of this resonance are determined as 11.497(2) eV and 1.3(2) meV, respectively. <i>Ab initio</i> potential energy curves are obtained from CCSD(T) calculations for the neutral N₂(X¹Σ⁺<sub>g</sub>) and N*₂(E³Σ⁺<sub>g</sub>) states as well as for the N⁻₂(R²Σ⁺<sub>g</sub>) resonance state. They corroborate quite accurately the measured resonance energy and provide accurate energy spacings and overlap integrals for the pertinent vibrational states. A detailed analysis of resonance line shapes for selected scattering angles is performed by applying a model for the interference of resonant and nonresonant scattering processes. It provides a link between the resonance width to absolute DCS and describes elastic and vibrational excitation processes on a common basis. Through both their size and sign, vibrational overlap integrals are shown to determine the observed Fano-type line shapes and account for the opposite asymmetries and intensity changes of adjacent vibrational resonance peaks. Fine-tuning of the fits to the observed shapes is achieved by proper parametrization of the nonresonant amplitudes. A highly resolved excitation function for the formation of the metastable N*₂(E³Σ⁺<sub>g</sub>) level from threshold (near 11.88 eV) to 13.4 eV is also presented.
2009-11-12T15:51:28Z
http://doc.rero.ch/record/12946