Three-body association reactions of NO+ and O+2 with N2

The cluster ions NO+ (N2)n, n≤5, and O+2 (N2)n, n≤6, were observed in a N2–O2 gas mixture irradiated by α particles. The temperature dependence of equilibrium constants K for association reactions X+(N2)n−1+2N2⇄X+ (N2)n+N2, X=NO, O2, was determined using high-pressure mass spectrometry. With X=NO, the enthalpies and entropies of clustering (−ΔH°, kcal/mol;−ΔS°, cal/mol K) are found to be (4.4; 13.3) and (3.9; 12.6) for n=1 and 2, respectively. Estimation of K at 204 K yields 1.1×10−2 (±30%) Torr−1 for n=3 and ∼4×10−3 Torr−1 for n=4. For X=O2, the (−ΔH°;−ΔS°) values, for n=1, 2, 3 are (5.20; 15.8), (4.3; 13.8), and (3.46; 12.1), respectively. The value of K (n=4) is estimated to be ∼ 4×10−2 Torr−1 at 184 K, and ∼7×10−3 Torr−1 at 204 K; for n=5, K is ∼1×10−2 Torr−1 at 184 K. The results for n=1 are compared with previously reported measurements.