A C Faraday Rotation of Aqueous Iron (III) Chloride

Authors:  J .Moore, M. Syed , and D. Morris
Date:  February 2013


Despite the many applications of Faraday Rotation (FR)  in optics and communications, the significance of this magneto-optic effect in chemical analysis has not been fully explored.  This study seeks to assess the effectiveness of FR inlearning about the principles of chemical equilibrium and reaction kinetics.  The dependence of the Verdet constant on the concentration of FeCl3 in aqueous solution was investigated at 633 nm using Alternating Current (AC) FR.  The AC technique, which has been used in several other studies, utilizes lock-in detection which allows for the reliable determination of exceedingly small rotation angles, which in turn can be used to determine the Verdet constant of a given sample.  The Raman spectra of each sample was also collected using an excitation wavelength of 785 nm.  The FR results showed the solution changing from a diamagnetic state to a paramagnetic state, and identified the magnetic transition concentration to be about 1.5 M.  The data also showed that the Verdet constant deviates slightly from a linear dependence on solution concentration, suggesting that the relative concentration of species is complex even for simple compounds.  Basic Raman spectral analysis confirmed the growth of paramagnetic species, but was not able to detect nonlinearity as clearly as FR.  We conclude that FR, when used in conjunction with a well-established technique such as Raman spectroscopy, has the potential to contribute useful complimentary data for chemical analysis.