Precise Determination of Frequency Shifts by Raman Difference Spectroscopy Using Voigt Profile for the Raman Band

Abstract

A convenient method for the precise determination of the frequency shifts from experimentally obtained Raman difference spectra is described. The method is based on the explicit calculation of the difference curve taking Voigt profile for the Raman band. A relationship between Δ/T (Δ, frequency separation between two Raman bands, Γ, Raman bandwidth) and d/I0 ( d, peak-to-peak height in the difference spectrum; I0, Raman band height) is presented in a graphical form as a function of the band shape parameter Γ/Γ G [Γ G = (Δν1/2)slit: used slit width determined experimentally by measuring the half-bandwidth of a narrow plasma line]. The experimental determination of (Δν1/2)slit, Γ, d, and I0 then allows direct derivation of Δ/Γ from the graphically presented functions and consequently the actual frequency shift Δ. The value of Δ/Γ can usually be determined with a typical uncertainty of ±0.002 in the small frequency shift limit and ±0.005 for medium and large frequency shifts and these would determine the frequency shift, Δ, with a maximum uncertainty of ±0.02 cm−1. An example of experimental spectra has been analyzed in order to assess the utility of the present technique.