Dissociative excitation of N2 by electron impact: Translational spectroscopy of long-lived high-Rydberg fragment atoms

Nitrogen atoms in long-lived high-Rydberg states have been produced in the dissociative excitation of N2 by electron impact. Four principal features were found in the time-of-flight distributions of the dissociation fragments and in the corresponding translational (kinetic) energy distributions. Appearance potentials and excitation functions were measured for high-Rydberg atoms with known and well-defined translational energies; for the slowest high-Rydberg fragments the excitation function exhibits sharp, resonancelike structure near threshold. The core-ion model of high-Rydberg dissociation, which treats the Rydberg electron essentially as a spectator in the dissociation process, is described and used to interpret the data. Observed dissociation limits are assigned as one fragment being an N+(3P) core surrounded by a high-Rydberg electron and the other fragment being a nitrogen atom or ion. In addition, the high-Rydberg translational energy distributions are in reasonable qualitative agreement with kinetic energy distributions of N+ measured by dissociative ionization experiments. These observations provide substantial support for the core-ion model. The available data on the dissociative core-ion states of N2+ are discussed extensively. However, no unique assignments can be made for the molecular high-Rydberg states which participate in the dissociation processes.