Structures and binding energies of proton-bound pairs of HCN and CH3CN with NH3, H2O, HF, CH3NH2, CH3OH, and CH3F

In this study, 12 nitrile-containing proton-bound dimers were investigated with ab initio molecular orbital calculations: (HCN)(NH3)H+, (HCN)(H2O)H+, (HCN)(HF)H+, (HCN)(CH3NH2)H+, (HCN)(CH3OH)H+, (HCN)(CH3F)H+, (CH3CN)(NH3)H, (CH3CN)(H2O)H+, (CH3CN)(HF)H+, (CH3CN)(CH3NH2)H+, (CH3CN)(CH3OH)H+, and ( CH3CN)(CH3F)H+. The geometries of these dimers were optimized at the MP2/6- 31+G-(d) level of theory, and their binding energies (relative to the lowes t energy dissociation products) were calculated with the G2, G2(ZPE=MP2), G 2(MP2), and G2(MP2,SVP) methods. The trends in the binding energies follow the absolute value of the difference in proton affinity of the constituent monomers; the larger the PA difference, the smaller the binding energy. An empirical relationship has been derived that may prove useful in predicting the binding energies of other nitrile-containing cluster ions. The results are compared to experimental values where available.