Optically Forbidden Excitations of 2s Electron of Neon Studied by Fast Electron Impact

The electron energy loss spectrum in the energy region of 42--48.5eV of neon is measured with an angle-resolved fast-electron energy-loss spectrometer at an incident electron energy of 2500eV. Besides the dipole-allowed autoionization transitions of 2s^-1np(n=3,4) and 2p^-23s3p, the dipole-forbidden ones of 2s^-1ns(n=3-6) and 2^-13d are observed. The line profile parameters, i.e. E_r, Γ and q for these transitions, are determined, and the momentum transfer dependence behaviour is discussed.