Electron-impact excitation cross sections of K*(3p54s22P3/2,2P1/2) autoionizing states: strong fine-structure dependence near threshold

The electron-impact cross sections of the inner-shell excited autoionizing states K*(3p 5 4s 2 2 P 3/2 ) and K*(3p 5 4s 2 2 P 1/2 ) were measured for the incident energy ranges from threshold up to 1 keV and up to 37.2 eV, respectively. A strong negative-ion resonance structure was found in the excitation cross section of the 2 P 3/2 state close to the threshold, whereas the excitation function of the 2 P 1/2 state is rather smooth. For impact energies below 40 eV the cross section ratio R of the fine-structure components shows a substantial energy-dependent deviation from the statistical value R = 2. The present experimental values are compared with recent theoretical results obtained in the distorted-wave Born approximation.