Determination by Gas-Phase EPR of the Absolute Concentration of Species Undergoing Electric Dipole Transitions

Publisher Website
Google Scholar
Abstract
An experimental investigation of the theoretical expressions relating gas‐phase EPR signal strengths and absolute concentration of species undergoing electric dipole transitions has been carried out. Absolute concentrations of SO(3Σ−) have been determined by EPR using NO as a calibrant gas. Concomitant determinations by titration of SO(3Σ−) with known amounts of NO2 are found to be in excellent agreement with the EPR results, once inconsistencies in the published values for the transition moments of NO(2Π) and SO(3Σ−) are reconciled. The agreement supports the validity of each technique, but the EPR method is more convenient once a correct calibration factor is established. Several methods for determining the signal strength from an observed EPR line (first moment, double integral, width squared times height) have been critically examined. All of the methods were found to yield consistent results when properly applied. A choice among them will be dependent upon the particular requirements of any given experiment.