Beyond Beer's Law: Revisiting the Lorentz-Lorenz Equation
Mayerhoefer TG, Popp J (2020)
Publication Type: Journal article
Publication year: 2020
Journal
Book Volume: 21
Pages Range: 1218-1223
Journal Issue: 12
Abstract
In this contribution we show how the Lorentz-Lorenz and the Clausius-Mosotti equations are related to Beer's law. Accordingly, the linear concentration dependence of absorbance is a consequence of neglecting the difference between the local and the applied electric field. Additionally, it is necessary to assume that the absorption index and the related refractive index change is small. By connecting the Lorentz-Lorenz equations with dispersion theory, it becomes obvious that the oscillators are coupled via the local field. We investigate this coupling with numerical examples and show that, as a consequence, the integrated absorbance of a single band is in general no longer linearly depending on the concentration. In practice, the deviations from Beer's law usually do not set in before the density reaches about one tenth of that of condensed matter. For solutions, the Lorentz-Lorenz equations predict a strong coupling also between the oscillators of solute and solvent. In particular, in the infrared spectral region, the absorption coefficients are prognosticated to be much higher due to this coupling compared to those in the gas phase.
Involved external institutions
Germany (DE)How to cite
APA:
Mayerhoefer, T.G., & Popp, J. (2020). Beyond Beer's Law: Revisiting the Lorentz-Lorenz Equation. ChemPhysChem, 21(12), 1218-1223. https://doi.org/10.1002/cphc.202000301
MLA:
Mayerhoefer, Thomas G., and Juergen Popp. "Beyond Beer's Law: Revisiting the Lorentz-Lorenz Equation." ChemPhysChem 21.12 (2020): 1218-1223.
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