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

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Abstract
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.