PROPERTIES OF CLUSTERS IN THE GAS-PHASE .3. HYDRATION COMPLEXES OF CO3- AND HCO3-

Employing high-pressure mass spectrometry, the ΔH°n, n+1 and ΔS°n, n+1 for the gas-phase reactions A-(H2O)n + H2O = A-(H2O)n+1 (where A- = CO3- and HCO3-) were measured from n=0 to n=2 and 3, respectively. In the case of CO3-, comparison of ΔG° n, n+1 (n= 0, 1) derived from these data at 296 K shows good agreement with previous measurements made only at that single temperature (Fehsenfeld and Ferguson). As an aid in understanding the bonding resulting from hydration of the ions, CNDO/2 calculations on the HCO3-H2O system were also performed and the results are discussed herein. In particular, the magnitude of the bonding for one and two water molecules to HCO3- at different sites is discussed. The gas-phase results, when compared with those for other negative ions, have revealed interesting features and have led to a determination of the lower bound for the aqueous phase total single ion hydration energy of HC03-. © 1979, American Chemical Society. All rights reserved.