Electron-impact excitation of potassium autoionizing levels in the near-threshold region

Abstract

The metastable excitation function and the near-threshold energy loss spectrum in potassium, corresponding to 3p 6 core excitation, have been measured over the energy range 18-24 eV. Many structures have been observed for the first time in the metastable excitation function. From a comparison of the observed yields of metastable atoms and scattered electrons, various processes for metastable production are considered, including resonance excitation and radiative cascade. The excitation thresholds for the lowest-lying metastable autoionizing levels in potassium, namely 3p 5 4s4p 4 D 7/2 and 3p 5 3d4s 4 F 9/2 , have been determined to be 20.28 ± 0.05 eV and 20.42 ± 0.05 eV, respectively.

Excitation of autoionizing states in potassium by electron impact

“…The cascade contribution into the (3p 5 3d4s) 4 P 3/2 level, on the other hand, could be revealed in the initial part of its excitation function, in particular in the low-energy wing of the nearthreshold resonance at 21.1 eV. However, in order to reveal this process, the additional measurements should be performed with a The presence of the resonance features in all measured excitation functions just confirms the earlier observations [5][6][7] of the important role of negative-ions in electron impact excitation of the 3p 6 -subshell in potassium. The threshold resonance at 21.1 eV, observed in the excitation function for the (3p 5 3d4s) 4 P 3/2 , level may reflect the formation of a negative-ion state with a tentative configuration 3p 5 3d4s 2 .…”

“…Also, the role of cascade processes has been discussed in the excitation of the quartet states. The total excitation cross-section for the (3p 5 4s 2 ) 2 P 1/2,3/2 lowest autoionizing doublet has been measured recently in [3,7] with the energy spread of the incident electrons equal to 0.7 and 0.25 eV, respectively. Using the results of extended R-matrix calculations, a strong near-threshold structure has been attributed by the authors also to the negativeion resonances.…”

Resonance excitation of autoionizing states in alkali atoms by electron impact

“…Важливим результатом проведених досліджень є також визначення порогів збудження та спектроскопічна класифікація метастабільних рівнів в атомах калію [34] та рубідію [35]. На початок цих досліджень в цьому питанні існувала неоднозначність як в енергетичному положенні, так і спектроскопічній класифікації таких рівнів.…”

Electron excitation of the valence subshell in potassium at low impact energies

“…The successful application of electron energy-loss spectroscopy for studying the 3p 5 n 1 l 1 n 2 l 2 autoionizing states in potassium was reported earlier [1]. Up to date, the energy-loss spectra of the 4s-valence subshell have been studied only for electron impact energies of 7 eV and above ( [2] and references therein).…”

“…The electron spectrometer and measuring procedure were described in detail elsewhere [1]. The measurements were performed at an observation angle of 90º and an overall energy resolution of 0.07 eV.…”