Collective Motion of Charges in Lithium Tetrafluoroborate Solutions in Acetonitrile

Abstract

The spectra (cosine Fourier transform) of autocorrelation functions of a microscopic current and their components in lithium tetrafluoroborate solutions in acetonitrile at concentrations of up to 0.75 M are studied by molecular dynamic modeling. The contributions of molecules (M), cations (Kt), and anions (An) to the overall spectrum are determined. The latter is presented as the sum of series of components (MM, MKt + KtM, MAn + AnM, KtKt, KtAn + AnKt, AnAn). The maximums in the MM component at 14 THz and KtKt component at 55 THz are related to IR bands in the spectrum. A negative peak is observed in the (KtAn + AnKt) component at 4 THz. A “microscopic” interpretation is provided for relevant spectra in the terms of intermolecular and ion–molecular interactions. The link between the spectra of the current autocorrelation functions and the nature of ionic association is explained.