Far-infrared and Raman investigation of LiNO3and NaNO2in the liquid state

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Abstract
The far-infrared (FIR) reflection spectra of molten LiNO3 and NaNO2 are measured from 13 to 530 cm-1 and from 13 to 350 cm-1 respectively. Data from microwave and millimetre-wave measurements between 0.3 and 5 cm-1 are added to extend the spectra to zero frequency. The dielectric function epsilon ( omega ) and the optical conductivity sigma are derived from a Kramers-Kronig analysis of the reflection spectra. These functions exhibit a strongly damped oscillatory response. The FIR conductivity can be well described by a generalised oscillator equation containing a sum of two exponentials as the memory function. Results of additional AC measurements up to 10 GHz and the millimetre-wave data reveal the shape of sigma in the transition region from oscillatory to diffusive behaviour. The Raman spectra of the ionic liquids are measured between 0 and 300 cm-1. Scattering of residual lattice modes is observed superimposed on Rayleigh wing scattering. In NaNO2 the variation of the spectra of the lattice modes in the solid-to-liquid transition is studied.