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.