Time-ordering effects in K-shell excitation of 170-MeV Ne7+ colliding with gas atoms: Single excitation.

Abstract

The method of 0\ifmmode^\circ\else\textdegree\fi{} Auger spectroscopy was applied to measure state-selective K-shell excitation in Li-like ${\mathrm{Ne}}^{7+}$ incident with 170 MeV on ${\mathrm{H}}_{2}$, He, ${\mathrm{CH}}_{4}$, Ne, and Ar. The high-resolution technique allows for the separate analysis of the states $_{\mathit{a}}^{2}$P and $_{\mathit{b}}^{2}$P whose dominant components are 1s(2s2p $^{3}$P${)}^{2}$P and 1s(2s2p $^{1}$P${)}^{2}$P, respectively. The results are used to study time-ordering and interference effects in the process of single excitation. For the state 1s(2s2p $^{3}$P${)}^{2}$P it is found that the phenomenon of Pauli blocking inhibits the loss of time ordering, whereas dealignment effects diminish interferences between first- and second-order mechanisms. The 1s(2s2p $^{1}$P${)}^{2}$P state involves partial loss of time ordering; however, non-spin-flip rules recover sufficient time ordering so that interference effects can be observed. The semiclassical approximation is used up to second order to provide conclusive evidence for the measured interference effects.