Electron Spin Resonance Studies of Silver Atom Solvation in Ethanol-Water Mixtures. Evidence for Preferential Solvation

Article abstract of DOI:10.1021/j100459a006

Frozen solutions of silver perchlorate exposed to (60)Co γ irradiation at 4 K form silver atoms by reaction of radiation-produced electrons with the silver ion.At 4 K the silver atoms are initially produced in a nonequilibrium or presolvated state, and upon brief warming to 77 K the first solvation shell geometry changes to produce an equilibrium or solvated silver atom.The presolvated and solvated silver atoms in water and ethanol matrices are characterized by different isotropic hyperfine couplings and line widths measured by electron spin resonance.We have investigated silver atoms in water-ethanol mixtures to search for preferential solvation effects.From 0 to 13 mol percent ethanol the presolvated silver atom formed at 4 K exhibits parameters characteristic of a water environment.At 13 mol percent the parameters suddenly change to those characteristic of an ethanol environment.This suggests that the original silver ion undergoes a drastic change in its first solvation shell at 13 mol percent ethanol.This dramatic change appears to correlate with the minimum in the excess enthalpy of mixing of ethanol and water vs. ethanol mole percent.Further solvation changes occur on thermal annealing the silver atoms at 77 K.