A study of the collisional dissociation of H2+ions with a flight-time difference method

Abstract

Describes a flight-time difference method for the measurement of the velocity distributions of fragment pairs resulting from collisional dissociation of molecular ions in the keV range. Both dissociation fragments are detected in coincidence with respect to their flight-time difference, scattering angle and charge. Using this method velocity distributions were measured of the H-H, H-H⁺ and H⁺-H⁺ fragment pairs arising from collisional dissociation of 10 keV H₂⁺ ions, the centres-of-mass of which were scattered in collisions with H₂ molecules by less than 0.1 degrees . H-H fragments can be ascribed to dissociations in the lowest ³ Sigma _u⁺ state of H₂. The H-H⁺ fragments essentially come from dissociations in the 2p sigma _u state of H₂⁺. In addition some arise from H₂⁺ ions lying prior to collision in highly excited vibrational and rotational states just below the dissociation limit of the 1s sigma _g ground state. H⁺-H⁺ fragment pairs did not appear in dissociations of 10 keV H₂⁺ ions incident on H₂.