GAS-PHASE EQUILIBRIA STUDIES OF C2H2N+ AND C3H4N+ WITH CH3CN

Thermodynamic quantities, Delta H(n-1,n)degrees and Delta S(n-1,n)degr ees, for the gas-phase clustering reactions of C2H2N+ and C3H4N+ With CH3CN have been studied using a pulsed electron beam high-pressure mas s spectrometer. For the C2H2N+(CH3CN)(n) clusters studied, in the firs t step the C2H2N+ ion was seen to disappear rapidly after the electron pulse and the equilibrium of this ion for the reaction forming C2H2N. CH3CN was not observed under conditions of the experiments. In the c ase of C3H4N+(CH3CN)(n), the -Delta H(n-1,n)degrees values show a larg e gap with n=1 --> 2, suggesting that the adduct ion, C3H4N+. CH3CN, i s a core in the cluster. Comparison of the bond enthalpies of C2H2N+(C H3CN)(n less than or equal to 5) and C3H4N+(CH3CN)(n less than or equa l to 4) with those of alkali metal ions solvated by CH3CN shows that a t n greater than or equal to 2 the ion-ligand interaction in the clust ers is mainly electrostatic. (C) 1998 Elsevier Science B.V. All rights reserved.