Electronimpact cross sections for the 22P state excitation of lithium

Abstract
Electron impact excitation of the 2p 2P state of Li was studied at 10, 20, 60, 100, 150 and 200 eV. Relative differential cross sections in the angular range 3-120 degrees were measured and then normalised to the absolute scale by using the optical f value. Integral and momentum transfer cross sections were obtained by extrapolating the differential cross sections to 0 degrees and to 180 degrees . The question of normalising electron-metal-atom collision cross sections in general was examined and the method of normalisation to optical f values in particular was investigated in detail. It has been concluded that the extrapolation of the apparent generalised oscillator strength (obtained from the measured differential cross sections) to the zero momentum transfer limit with an expression using even powers of the momentum transfer and normalisation of the limit to the optical f value yields reliable absolute cross sections.