Excitation of the 2pπu state of H2+ as a function of alignment of the molecular axis

The relative cross section for the excitation of the 2p pi(u) state of H+ as a function of the orientation of the internuclear axis is measured and calculated. 400 eV electrons bombard an H-2 target. Electrons scattered at 18 degrees with an energy loss of 41 eV are detected in coincidence with H+ fragment ions of energy 4.9 eV. Measurement of the scattering angle and energy lass establishes the momentum transfer vector of the collision K and the scattering plane. The angular distribution of 3.9 eV H+ ions relative to K is recorded. Because the rotation time of H-2 is long compared to the dissociation time, it follows that the H+ ions leave the collision region along the line of the internuclear axis at the time of the collision. The relative cross section peaks when the internuclear axis is perpendicular to K. Calculations predicting the shape of the angular distribution fit the data.