Excitation of the 2p sigma(u) state of H-2(+) as a function of energy loss

The relative cross section for the excitation of the 2p sigma(u) state of H -2(+) by 400 eV electrons as a function of energy loss has been measured an d calculated. Electrons scattered at 18 degrees with energy losses ranging from 30 to 72 eV were detected in coincidence with H+ ions of 7.7 eV. The H + ions were detected at 72 degrees relative to the beam direction. Because of the rapid dissociation of the excited state, it follows that the detecte d ions were produced by target H-2. molecules with internuclear axes orient ed at 72 degrees. The relative cross sections were calculated using prolate spheroidal coordinates and fitted to the data with one parameter. The gene ral shape of the energy-loss curve is in agreement with the measurements.