Dissociative-recombination and excitation measurements with <emb><base>H</base>^n+>₂</emb> and <emb><base>HD</base>⁺</emb>s

The cross sections for dissociative recombination (DR) and dissociative excitation (DE) have been measured for the H^n+>₂ and HD⁺ molecular ions in the energy range from 0 to ∼30 eV. An imaging technique that provides a measure of the kinetic energy release in the DR process was used to yield information about the initial vibrational distribution of the molecular ions and the final atomic states of the DR reaction. The results for DR with HD⁺ in the vibrational ground level, ν=0, are compared with other measurements and recent multichannel quantum defect theory calculations. Significant deviations that appear at high energy ∼5–10 eV are discussed. The present work reports on an absolute DE measurement with HD⁺ . The vibrational distribution of H^n+>₂ was manipulated by photodissociation of ions in vibrationally excited levels. We obtained DE and DR cross sections for H^n+>₂ ions populating primarily the two lowest vibrational levels ν=0,1 and H^n+>₂ ions in a broad vibrational distribution. It is found that DR of H^n+>₂ with zero energy electrons results in the H(n=1)+H(n=2) final channel, open for all vibrational levels, and in the H(n=1)+H(n=3) channel, which is energetically open for initial vibrational levels ν⩾5.