Semi-empirical and ab initio calculations are reported which provide a possible explanation for reported experimental results on 2-photon ionization of NO containing a few percent of N2O, which found (NO)3(N2O)n+or−clusters to be significantly more abundant than other (NO)m(N2O)n products. It is found that the observed abundances of (NO)3(N2O)n ionic clusters may be accounted for by the existence of covalent cyclic trimers of nitric oxide attached to oligomers of nitrous oxide. The extra stability of NO trimers in the observed clusters appears to arise from (NO)3+ rather than (NO)3. Attachment of an (N2O)n side chain to (NO)3+ occurs exothermically. It is suggested that the addition of N2O to cyclic-(NO)3+ might provide a means of making a polymer of nitrous oxide, which could have useful properties.