Attenuated total reflection: A new principle for the production of useful infra-red reflection spectra of organic compounds

Abstract

Infra-red reflection spectra of exceptionally good contrast can be obtained if the interface between a dielectric of high refractive index and the sample is taken as the reflecting surface. Radiation incident from the strongly refracting dielectric on this interface at an angle somewhat larger than the critical angle will be totally reflected, but only in those frequency regions where the second medium is non-absorbing (κ = 0). In regions with κ ≠ 0, reflection will not be total any more and, accordingly, a reflection spectrum of high contrast and intensity is obtained, which strongly resembles a transmission spectrum. These spectra may, after calibration, be used as such for quantitative purposes. They may also, by graphical methods or by application of the Kramers-Kronig relation, be converted into spectra of the optical constants n and κ.