Deconvolution of lorentzian Raman Linewidth: Techniques of polynomial fitting and extrapolation

A simple, convenient and precise technique for deconvolving the Lorentzian (true) Raman linewidth, Γ_L, from the observed Raman linewidth, (Δ_1/2)_R [the FWHM (full width at half‐maximum) of the Raman line in question], through polynomial fitting, was developed. The precision of this technique is a consequence of the fact that the values of Γ_L/(Δ_1/2)_R (= Y), obtained by exact numerical evaluation of the Voigt profiles for the Raman bands, were flitted to third‐ and fourth‐degree polynomials in S/(Δ_1/2)_R (= X), S being the spectral slit width measured as the linewidth (FWHM) of a narrow spectral line recorded at the same slit settings as the Raman line. The procedure of obtaining Γ_L, from the knowledge of S,(Δν_1/2)_R and X, which yields better results, is discussed. Another technique of deconvolution is described and discussed, involving the measurement of Raman linewidths of a particular Raman line for about five or six different slit widths. The measured linewidths (Δ_1/2)_R, when extrapolated to S → 0, give the value of Γ_L directly. A careful comparison with the other deconvolution techniques reveals that the method of polynomial fitting is relatively more precise than other semi‐analytical deconvolution techniques, and the extrapolation technique also gives reasonably good results. The applicability of both methods was tested by taking some selected Raman lines.