Electron impact excitation cross sections of sodium 2p53s2 2P autoionizing state from threshold to 1.5 keV

Relative excitation cross sections of the lowest-lying autoionizing state 2p(5)3s(2) P-2 Of sodium are measured for electron impact in the range of incident energy E-0 from 1.5 keV down to the threshold. Absolute cross sections are obtained by normalization of the relative cross sections at E-0 = 1.5 keV to the theoretical cross section in the plane-wave Born approximation with accurate atomic wavefunctions. Negative ion resonances near the excitation threshold are observed and reproduced by a 26-state R-matrix calculation. The cross sections at intermediate incident energies are obtained in the distorted-wave Born approximation and are compared with the present experimental values and with theoretical values of other authors.