Proton affinities in water of maingroup-element hydrides - Effects of hydration and methyl substitution

We have computed the proton affinities in water of archetypal anionic and neutral bases across the periodic table using the generalized gradient approximation (GGA) of density functional theory (DFT) at BP86/QZ4P//BP86/TZ2P. The main purpose of this work is to provide an intrinsically consistent set of values of the 298-K proton affinities in agueous solution of all anionic (XH_n-1^-) and neutral bases (XH_n) constituted by maingroup-element hydrides of groups 14-17 and the noble gases (i.e., group 18) along the periods 1-6. Hydration has little effect on the trends in PA values, especially in the case of the neutral bases. However, in the case of the anionic bases, hydration drastically reduces the magnitude of the PA values. Finally, we have studied how proton affinities in water are affected by methyl substitution at the protophilic center.