ESS 51 F2013 lecture 15 spectroscopy Watenphul

Ance t is dened by the ra6o of the intensity of the

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Unformatted text preview: 6o of the intensity of the transmi?ed light IIR to the intensity of the incident light I0 T = IIR / I0 The rela6ons between intensity IIR and absorp6on A are given by IIR = I0 . 10–A T = 10–A A = – log T detector IR source IR spectrum of gypsum CaSO4 . 2H2O ν2 ν1 ν3 vibra6onal modes free of TO4 groups stretching vibra6ons bending vibra6ons vibra6onal modes free of TO4 groups stretching vibra6ons not IR ac6ve IR ac6ve bending vibra6ons IR spectra of crystal laece vibra6ons Spectral range 400 – 1400 cm–1 gives a fingerprint and can be used for mineral iden6fica6on –> comparison with databases IR spectra of OH-­‐bearing minerals SiO4 groups CO3 groups OH groups IR spectra of OH-­‐bearing minerals 3675 cm–1 3425 cm–1 3610 cm–1 IR spectra of OH-­‐bearing minerals The frequency of the OH-­‐vibra6on band is correlated with the O–H … O bond length of the mineral. Quan6fica6on of the OH-­‐content The Lambert–Beer law A = ε t c correlates the absorbance A with the sample thickness t and the concentra6on c of the oscilla6ng species (e.g. OH). The scaling factor ε is called molar absorp6on coefficient....
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