Unusual angular momentum transfer in electron-impact excitation of neon

Abstract

We report results from a joint experimental/theoretical study of the angular momentum transfer in electron impact excitation of the (2p 6) 1 S0 → (2p 5 3s) 1 P1 resonance transition in Ne. Both the measured and calculated data show the circular light polarization P3 to be positive for an incident energy of 25 eV at scattering angles below 40 •. This observation implies a negative angular momentum transfer L ⊥ , which is the opposite sign of orientation expected from a well-known propensity rule for S → P excitation at small scattering angles.

Polarization correlations for electron-impact excitation of the resonant transitions of Ne and Ar at low incident energies

“…Table 1 shows a summary of our experimental results. Figure 2 exhibits our polarization correlation parameters for Ne at E 0 = 25 eV, which were also reported in [38]. For the linear polarization parameters, the DWBA [29] and the present BSR and RDW models show excellent agreement with each other as well as with the present experiment, which is restricted by statistics to θ < 40 o .…”

“…shows very good agreement with the BSR predictions for Ne, which motivated this project. As reported in [38], the BSR only predicts positive 3 P values if it includes channels exceeding the minimum 5-state model (the 2p 6 ground state plus the four fine structure states of the 2p 5 3s configuration). Such channelcoupling is not prevalent in the DWBA, which shows the usual 3 P form predicted by [8], although the drop in 3 P from zero is less dramatic than what is usually observed at higher E 0 values.…”

TheB-splineR-matrix method for atomic processes: application to atomic structure, electron collisions and photoionization

“…Bottom: circular light polarization P 3 for the corresponding lowest 1 P 1 states in Ne, Ar, Kr and Xe, as predicted by BSR calculations with a sufficient number of states for convergence. (Reproduced with permission from[75]. © 2012 by The American Physical Society.)…”

Benchmark Angle-Differential Cross-Section Ratios for Excitation of the 4p5s Configuration in Krypton

“…Our findings might also help to interpret the reversal of the angular momentum perpendicular to the scattering plane, (L ⊥ ), imparted to the target. This was found at similarly small θ in the excitation of the resonance transition in Ne [38], i.e., of the 2p 5 3s[3/2] 1 LScoupled 1 P 1 component, which is again mixed (but to a lesser extent) with the LS-coupled 3 P 1 component. It is the latter's excitation via spin-exchange that could enable a physical explanation for the reversal of L ⊥ compared to the case for a direct singlet → singlet excitation.…”