Resonant Auger decay of Ar 2 p 3 / 2 − 1 4 s and 2 p 3 / 2 − 1 4 p states excited by electron impact

Auger spectra of resonantly excited 2p{sub 3/2}{sup -1}4s and 2p{sub 3/2}{sup -1}4p states in argon were measured by (e,2e) technique. The 99.2-eV scattered electrons were detected in coincidence with L{sub 3}-M{sub 23}M{sub 23} Auger electrons, and the experiment was performed at 343.6- and 344.9-eV electron impact to tune the energy loss to the energy of the dipole-allowed and the dipole-forbidden excitations, respectively. The resonant Auger spectra are obtained upon subtraction of the overlapping signal due to the outer-shell ionization, which was recorded at 340-eV electron-impact energy. The most intense groups of Auger transitions from 2p{sub 3/2}{sup -1}4s (J=1,2) and 2p{sub 3/2}{sup -1}4p (J=0,1,2,3) states are identified by comparison with the results of the two-step model, based on distorted-wave Born approximation with exchange and multiconfiguration descriptions of the relaxed states. The 4 s spectrum displays a substantially larger shake-up contribution than the one observed in photoexcitation experiments, which may be explained by the interference of the resonant decay path with the direct ionization excitation of the Ar 3p subshell. The majority of the observed 4p signal is assigned to the monopole and quadrupole excitations of the ground state.

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