Mass spectrometric study of three-body ion-molecule clustering reactions of CpHq+ ions with N2 or CH4 in N2CH4 mixtures

Thermochemical data for several ion-molecule clustering of hydrocarbon ions with N2 or CH4 were obtained from clustering equilibria studies in gas mixtures irradiated by α-particles. High-pressure mass spectrometry was used to determine the enthalpy and entropy changes of clustering (ΔH° and ΔS°, respectively) for the reactions X+(N2)n−1+2N2⇋ X+(N2)n+N2 with X = CH5, n = 1–2; X = C2H5, n = 1–4; and X = C3H7, n = 1. For X = CH5, the values (ΔH°; ΔS°) are found to be (−6.8 kcal mol−1; −19.7 cal mol−1 K−1) for n = 1, and (−5.3 kcal mol−1; −15.9 cal mol−1K−1) for n = 2. For X = C2H5, (ΔH°; ΔS°) = (−6.9 kcal mol−1; −18.2 cal mol−1 K−1), for n = 1, and (−4.6 kcal mol−1; −20.8 cal mol−1 K−1) for n = 2. From the equilibrium measurements at 129 K, estimates of the thermochemical values could be obtained for n = 3–4. The results obtained for the free energy, ΔG°, were −1.4 kcal mol−1 for n = 3, and −1.1 kcal mol−1 for n = 4. For X = C3H7 we found ΔG° = −0.7 kcal mol−1 at 213 K. The association reactions X++2CH4⇋ X+(CH4)+CH4 with X = CH5, C2H5, C2H7, and C3H7 were also studied, resulting in free energy values at 206 K of −3.1, −1.9, −0.5 and −1.3 kcal mol−1, respectively. The results for CH5, C2H5 and C3H7 are compared with previously reported measurements.