Solvation of Cl⁻ and O₂⁻ with H₂O, CH₃OH, and CH₃CN in the gas phase

Abstract

Determination of the temperature dependence of the equilibrium constants K n ,n−1 for the reactions A − B n = A − B n−1 + B where A − equals Cl − and O 2 − and B is HOH, CH 3 OH, or CH 3 CN leads to the corresponding ΔH 0 n−1 , ΔG 0 n−1,n , and ΔS 0 n−1,n values. The experimental technique is based on mass spectrometric detection of ions escaping from a high pressure ion source. At n = 1, Cl − is solvated most strongly by methanol, then CH 3 CN and HOH. At higher n a cross over is observed with water becoming the best solvent. These results are in agreement with the positive transfer enthalpies and free energies for Cl − from the liquid solvents HOH → CH 3 OH and HOH → CH 3 CN reported in the literature.O 2 − is solvated more strongly than Cl − appearing thus as an ion of "size" intermediate between Cl − and F − Again CH 3 OH gives the highest interaction for n = 1, however for n > 1 water gives stronger interactions.