Photoabsorption Spectrum and Optically Forbidden Transitions of Krypton by Electron Impact

A high resolution fast electron energy loss spectrometer with multi-channel energy analysis was employed. The maxima just above the threshold 4p-1(2P1/2), which is regarded as a shape resonance, was obtained at 16.3 eV. The optically forbidden excitations of 4s electron were measured for the first time, and the energy positions are 23.75 eV (4s-15s), 25.66 eV (4s-16s/4d) and 26.60 eV (4s-17s/5d).