Applications of Group Theory: Infrared and Raman Spectra of the Isomers of 1,2-Dichloroethylene. A Physical Chemistry Experiment

Abstract

An experiment for the undergraduate physical chemistry laboratory, or an integrated analytical-physical laboratory, illustrates the application of spectroscopic selection rules for vibrational fundamentals as derived from group theory. The selection rules for the cis- and trans- isomers of 1,2-dichloroethylene are applied to assigning the vibrational fundamentals of these related but symmetrically distinct molecules. Applications of shapes of bands in gas-phase infrared spectra and of depolarization ratios of bands in liquid-phase Raman spectra are illustrated in making these assignments. The fundamental frequencies and the corresponding intensities in the infrared spectrum are compared with calculations made by DFT methods. Spectra are supplied in electronic format as part of the lab documentation.