Gas phase equilibria of ion-molecule clustering reactions between (C2H2)m+ ions and N2 were investigated by high-pressure mass spectrometry in N2-C2H2 mixtures irradiated by a-particles. Free energy values of clustering, DG0n-1, n, were obtained for reactions (C2H2)m+.(n-1)N2 + N2 <img border=0 width=32 height=32 src="../../../../../../img/revistas/jbchs/v8n3/a12img01.gif">(C2H2)m+.nN2, for different values of m and n. For m = 2, i.e., for the "core ion" (C2H2)2+, the values found for DG0n-1, n at T = 129 K are 0.87 ± 0.20 kcal/mol for (n-1, n) = (2,3) and 0.88 ± 0.20 kcal/mol for (n-1, n) = (3,4). For m = 3 ("core ion" (C2H2)3+), the free energy changes were found to be 0.91 ± 0.30 kcal/mol for (n-1, n) = (2,3), 0.73 ± 0.30 kcal/mol for (n-1, n) = (3,4); 0.65 ± 0.30 kcal/mol for (n-1, n) = (4,5), and 0.58 ± 0.30 for (n-1, n) = (5,6).
ion-molecule reactions; mass spectrometry; Titan atmosphere
