Unusual Spectral Behaviour of Ethanol Using Simple Xenon Lamp Excitation Source

Abstract

Raman scattering technique has been used in every field of research to determine purity of compounds or materials in different environments because every compound or material has the characteristic vibrations. In water and alcohol mixture, Raman scattering technique can be used. However, the behaviour of Raman scatterings was not addressed much when wavelength of excitation $(\lambda_{\rm exc})$ was considered at $2(\lambda_{\rm exc})$ or $(\lambda_{\rm exc})/2$. Excitations corresponding to $2(\lambda_{\rm exc})$ and $(\lambda_{\rm exc})/2$ are taken as the second order excitation and second harmonic excitation, respectively. Here, we report the following interesting observations in pure ethanol: (1) Raman scattering intensities after consideration of excitation at wavelength of second harmonic is slightly more than those of the direct excitation and (2) the peak intensity corresponding to wavelength of 2nd harmonic or 2nd order is very much less than that of Raman scattering. Spectral intensity decreases with increase of water content in ethanol. These observations are explained on basis of possible causes such as Raman or inelastic scattering from ethanol as well as photoluminescence from additive or foreign impurities present in ethanol.