Measurement of the Faraday effect and bond additivity in halogen-substituted methanes

Abstract

A sensitive photoelectric polarimeter incorporating a modulated magnetic field and lock-in detecting system was used to measure the Verdet constants in the vapour phase of the halogensubstituted methanes: trichlorofluoromethane, chlorotrifluoromethane, tetrafluoromethane, trifluoromethane, difluoromethane, fluoromethane, dichloromethane and chloromethane. Measurements were made at ten wavelengths in the visible spectrum from 406 to 633 nm. These and other results allow the testing of a scalar bond additivity model for the Verdet constant which in most cases produces agreement within 10 % of experimental values. Marked exceptions in difluoromethane and fluoromethane are suggestive of a fluorine anomaly, as is the Verdet constant of tetrafluoromethane which is less than half that of methane.