Abstract
Electron impact excitation of H2 and D2 within 0.05 eV of threshold is studied with a trapped‐electron method. An ac RPD technique is used to achieve energy resolution better than 0.1 eV. A series of trapped‐electron peaks is resolved in the 11.7‐ to 13.5‐eV range. These are identified as vibrational levels of the c 3Πu state. In this energy range, excitation of other states (both singlet and triplet) near threshold is found to be weak by comparison. Several peaks observed in the 13.8‐ to 15.4‐eV range could not be assigned to excitation of vibrational levels of a single electronic state.