Abstract
Absolute differential cross sections for electrons losing 10.2 eV in exciting the n=2 states of atomic hydrogen have been measured over the angular range 20 to 140 degrees for incident electron energies of 54 to 680 eV. The experimental apparatus, method and techniques are based upon those normally used in crossed electron and modulated atom beams experiments which study electron energy-loss spectra with good angular (2 degrees ) and energy (0.03 eV) resolution of the incident and scattered beams. Absolute cross section values have been determined by a method based on (i) a phase shift analysis of the elastic differential scattering of electrons from resonant states the (1s2s2)2S state in helium and the (3s23p54s2)2P3/2 and 2P1/2 states in argon and (ii) measurement of beam source pressures.