Alignment of the Na*2p53s22P3/2autoionizing state excited by electron impact: experiment and theory

The alignment of the 2p 5 3s 2 2 P 3/2 autoionizing state in sodium after electron-impact excitation was determined via the angular anisotropy of the intensity I ( ) of the autoionization electrons. For emission angles 90°, the intensities I ( ) were measured by rotating the incident electron gun, whereas magnetic-field deflection was applied for larger angles. Near-threshold negative-ion resonance structures in the alignment of an autoionizing state were observed for the first time and are discussed in detail. R -matrix calculations for incident electron energies from threshold to 80 eV successfully reproduced the broad-scale energy dependence of the alignment. The cross section ratio for the fine-structure components 2p 5 3s 2 2 P 3/2 and 2 P 1/2 were also measured and reproduced satisfactorily by theory.