Excitation of the Q11Σg+doubly excited state of H2by electron impact

400 eV electrons were used to excite the autoionizing state Q 1 1 Σ g + of H 2 . The relative cross section was measured as a function of: (1) the angle between the internuclear axis and the momentum transfer vector of the collision; and (2) energy loss for a fixed orientation of the molecular axis in the laboratory frame. In the first set of measurements electrons scattered at 18° with an energy loss of 29 eV were detected in coincidence with a 2 eV H + ion resulting from dissociation following autoionization. The angular distribution of the 2 eV ions was recorded and fitted to calculated values. A maximum was found when the internuclear axis was aligned with the momentum transfer vector. Secondly, the relative yield of 2 eV H + ions was measured as a function of energy loss in the electron-H 2 collisions. Energy loss ranged from 23 to 35 eV. The lowest lying Q 1 1 Σ g + , 1 Σ u + and 1 Π g were included in the calculated fit to the data.