Radiation Effects in Solid Nitrogen and Nitrogen-Containing Matrices: Fingerprints of N₄⁺ Species

The radiation effects and relaxation processes in solid N₂ and N₂-doped Ne matrices, preirradiated by an electron beam, have been studied in the temperature range of 5–40 and 5–15 K, respectively. The study was performed using luminescence methods: cathodoluminescence CL and developed by our group nonstationary luminescence NsL, as well as optical and current activation spectroscopy methods: spectrally resolved thermally stimulated luminescence TSL and exoelectron emission TSEE. An appreciable accumulation of N radicals, N⁺, N₂ ⁺ ions, and trapped electrons is found in nitrogen-containing Ne matrices. Neutralization reactions were shown to dominate relaxation scenario in the low-temperature range, while at higher temperatures diffusion-controlled reactions of neutral species contribute. It was conceived that in α-phase of solid N₂, the dimerization reaction (N₂ ⁺ + N₂ → N₄ ⁺) proceeds: “hole self-trapping”. Tetranitrogen cation N₄ ⁺ manifests itself by the dissociative recombination reaction with electron: N₄ ⁺ + e^– → N₂*(a^’1Σ_u ^–) + N₂ → N2 + N₂ + hν. In line with this assumption, we observed a growth of the a^’1Σ_u ^– → X¹Σ_g ⁺ transition intensity with an exposure time in CL spectra and the emergence of this emission in the course of electron detrapping on sample heating in the TSL and NsL experiments.