Elastic electron-alkali atom scattering near the first inelastic threshold

Resonance phenomena ine+-Li collisions

“…Threshold effect has been a focus of discussion for many decades [19,20], since Wigner first predicted the presence of cusp structures. Experimental observation and theoretical calculation have demonstrated the existence of threshold cusps for a low-energy electron collision with a lithium target (Eyb and Hofmann [21] and Burke and Taylor [22]). It is interesting to note a broad hump appearing near 1.90 eV in the D wave in the present CCO calculation, and this is maybe the overlap of the 2p threshold cusp and a D-wave resonance.…”

Observation of Threshold Effects in Positron Scattering from the Noble Gases

“…These cusps appear to be broader than those typically seen in electron scattering, with the positron features extending over a range of 1-3 eV, while cusps seen in electron scattering typically extend over 0.5 eV or less (see, for example, [2,3,5,15]). The observed features are almost certainly the result of virtual Ps formation, as has been suggested previously in the work of Coleman et al [12] as well as in the theoretical treatment of Meyerhof and Laricchia [10].…”

“…In the case of the alkalis [5], the cusp effects are seen at the opening of the strong n 2 P resonance transitions (e.g., n ¼ 3 for Na), which represent the overwhelming majority of the oscillator strength for these atoms [5]. The strong opening of these scattering channels is matched by marked cusp effects in the only other open channel, that for elastic scattering.…”

“…Indeed, the observation of threshold cusps for low energy electron scattering from the alkalis [5] provides an interesting comparison for the present investigation of positron interactions, in which we probe channel coupling at the threshold for positronium (Ps) formation. In the case of the alkalis [5], the cusp effects are seen at the opening of the strong n 2 P resonance transitions (e.g., n ¼ 3 for Na), which represent the overwhelming majority of the oscillator strength for these atoms [5].…”

Negative-ion resonances in total cross sections for slow electron-sodium collisions

“…Negative-ion formation in electronsodium (e-Na) scattering has attracted substantial theoretical and experimental efforts owing to its extreme sensitivity to the electron correlation effects. Experimental studies for sodium negative-ion resonances have been carried out in electron scattering [6][7][8][9][10][11][12], laser photodetachment technology [13], and electron transmission spectroscopy [14,15]. On the theoretical side, the low-lying negative-ion states were predicted by several different theoretical models, such as the close-coupling approach [16][17][18], the multiconfigurational Hartree-Fock method [19], and variational [20], effectiverange [21], and relativistic R-matrix techniques [22].…”