Surface enhancement Raman scattering from a silver electrode in amethyl acetate solution containing LiAsF₆ and(CH₃)₄NBr

摘要

The structure of the solvated lithium cation in methyl acetate(MA) and in acetone (AC) solutions has been investigated using Ramanspectroscopy. Evidence for contact ion pairing between Li⁺and AsF₆^- is also presented for both solvents. Thedegree of association is less for AC solutions. Surface enhanced Ramanscattering spectra of solvated lithium cation and tetramethylammoniumion (TMA⁺) in MA solutions adsorbed on a silver electrodehave been measured and compared to the normal Raman spectra of thecorresponding solution. Shifts in Raman frequencies for bothLi(MA)₄⁺ and the C₄-N symmetric andasymmetric stretching modes from TMA⁺ have been observed. Theresults show that (CH₃)₄N⁺ adsorbs to aAg electrode at low concentrations (5×10^-3 M)and positive potentials. Li(MA)₄⁺ also adsorbs onthe Ag electrode, but it appears to be replaced by(CH₃)₄N⁺ as the potential becomes morenegative. For the system Ag/MA, LiAsF₆ saturated withCO₂. Raman spectra of surface carbon have been recorded. Asimple model to illustrate the surface processes in this nonaqueoussystem and implications for lithium cell technology are presented