Autocorrelation analysis of infrared spectra from minerals

Abstract

The autocorrelation function, Corr(α, ω′) = \({\int}_{{-}{\infty}}^{{\infty}}\) α(ω + ω′)α(ω)dω, may be used to parameterise effective line widths of absorption bands in IR spectra. It has the advantage of not requiring any peak fitting to the primary spectra and can be applied to individual bands or groups of bands in a spectrum. A new procedure for analysing autocorrelation spectra which result from the application of the autocorrelation function to primary spectra is presented. The approach is well suited for quantifying line width variations in powder absorption spectra from sequences of samples with varying composition, degree of cation order or structural state. Worked examples are set out to illustrate different applications of the approach, including the characterisation of structural phase transitions in tridymite, Al/Si ordering under non-equilibrium conditions in Mg-cordierite, short range Al/Ge order in BaAl 2 Ge 2 O 8 feldspar and mixing behaviour in the jadeite-augite solid solution.