Thermochemistry from ion-molecule reactions of hydrated ions in the gas phase: a new variant of nanocalorimetry reveals product energy partitioning.

A new variant of nanocalorimetry is proposed for the thermochemical analysis of ion-molecule reactions of hydrated ions in the gas phase. The average number of water molecules evaporating during the reaction is extracted by quantitative modeling of the average number of water molecules in the reactant and product cluster distribution as a function of time, taking into account black-body radiation induced dissociation. The method is tested on reactions of (H2O)n(-) with O2 and CO2, and the core exchange reaction of CO2(-)(H2O)n with O2 to yield O2(-)(H2O)n and CO2. Reproducible results are obtained for the number of water molecules evaporating. Nanocalorimetric analysis reveals a non-ergodic component of DelatE(ne) = 59 +/- 14 kJ mol(-1) in the core exchange reaction, most likely carried away by the neutral CO2 product. Extrapolation to solution phase values suggests hydration enthalpies of DeltaH(hyd) = -375 +/- 30 kJ mol(-1) for O2(-) and DeltaH(hyd) = -268 +/- 27 kJ mol(-1) for CO2(-).