Negative Ion Formation by Thermal Electron Attachment to Nitrous Oxide at Atmospheric Pressure

Abstract

The time profiles of negative ions formed by X-ray irradiation in nitrous oxide at atmospheric pressure have been measured in the temperature range from 256 K to 500 K by using TRAPI. N₂O₂(N₂O)_n^- ions (0≤n≤8) and N₃O₂^- ions were observed but N₂O(N₂O)_n^- ions were not detected. The rates of negative ion formation were almost invariable for the different ionic species at the same temperature. The formation of the negative ions by thermal electron attachment was interpreted by the following processes; N₂O↔N₂O^* (vibrationally excited in bending mode), e_th^- + N₂O^-*↔N₂O^-*, N₂O^-* + N₂O → N₂O₂^- + N₂. The apparent activation energy of these processes was obtained to be 0.21 ±0.04 eV. The value of this activation energy corresponds to the excitation energy of the third vibrational level in the bending mode of N₂O. The formation of N₂O₂^- ions has been discussed in terms of the distribution of the cluster size (n) in N₂O₂(N₂O)_n^- ions and the activation energy which is lower than that of the dissociative resonance electron capture in N₂O (e^- + N₂O → O^- + N₂).