Ion-Clustering of the Cations in the High Energy Irradiation of Nitrous Oxide

• Published in: Radiation research 1973-12, Vol.56 (3), p.441-459
• Main Authors: Sieck, L. W., Gorden, R., Ausloos, P., Lias, S. G., Field, F.
• Format: Article
• Language: English
• Subjects: Atmospheric Pressure; Atoms; Cations; Electrons; Elementary Particles; Ions; Mass spectrometers; Mass Spectrometry; Molecules; Nitrous Oxide - radiation effects; Photoionization; Photons; Radiation Effects; Radiolysis; Reaction mechanisms
• ISSN: 0033-7587; 1938-5404
• DOI: 10.2307/3573715

The reactions of the positive ions in N2 O have been studied mass spectrometrically at pressures up to approximately 2 Torr and at temperatures in the vicinity of 300°K, that is, under conditions similar to those which prevail in a gas phase radiolysis experiment. The ${\rm N}_{2}{\rm O}^{+}$ parent ion associates with a N2 O molecule to form a $({\rm N}_{2}{\rm O})_{2}{}^{+}$ dimer, with a termolecular rate constant of $4.8\pm 0.5\times 10^{-28}\ {\rm cm}^{6}/\text{molecule}^{2}\text{-}{\rm sec}$ at 300°K. The ratio $({\rm N}_{2}{\rm O})_{2}{}^{+}/{\rm N}_{2}{\rm O}^{+}$ shows a sharp decrease with an increase in temperature. The NO+ fragment ion also associates with a N2 O molecule to form the ${\rm NO}^{+}\cdot {\rm N}_{2}{\rm O}$ association ion. At pressures greater than 1 Torr, this ion associates with a second molecule of N2 O to form ${\rm NO}^{+}\cdot ({\rm N}_{2}{\rm O})_{2}$. In order to investigate the effects of accumulated radiolytic products on the ionic mechanisms in N2 O, experiments were performed in which small amounts (∼0.1%) of O2, NO, and N2 were added to N2 O. In the presence of 0.1% O2, ${\rm O}_{2}{}^{+}\cdot {\rm N}_{2}{\rm O}$ is formed. In the presence of 0.1% NO, ${\rm NO}^{+}\cdot {\rm N}_{2}{\rm O}$ and $({\rm N}_{2}{\rm O})_{2}{\rm NO}^{+}$ were observed in much greater abundance than in pure N2 O, presumably from a reaction of ${\rm N}_{2}{\rm O}^{+}$ or $({\rm N}_{2}{\rm O})_{2}{}^{+}$ with NO molecules. The $({\rm NO})_{2}{}^{+}$ dimer ion was also observed in these experiments. No reactions of the positive ions in N2 O with N2 were observed. The results obtained in earlier pulse radiolysis and conventional low dose rate radiolysis experiments are reevaluated in order to take into account the formation of association ions. If one assumes that no dissociation occurs in the N2 O species formed by neutralization of $({\rm N}_{2}{\rm O})_{n}{}^{+}$ ions by ${\rm SF}_{6}{}^{-}$, it can be shown that observed pulse radiolysis results are consistent with the electron neutralization of $({\rm N}_{2}{\rm O})_{n}{}^{+}$ to give only one excited ${\rm N}_{2}{\rm O}^{\ast}$ species which dissociates; an alternate assumption about the neutralization mechanism involving ${\rm SF}_{6}{}^{-}$ leads to the conclusion that, on the average, 1.8 N2 O species dissociate for each $({\rm N}_{2}{\rm O})_{n}{}^{+}$ ion neutralized by an electron. In the low dose rate radiolysis, accumulated products may be expected to modify the ionic mechanism,