Infrared Spectrum and Group Theoretical Analysis of the Vibrational Modes of Carbonyl Sulfide

Carbonyl sulfide (OCS) is an excellent sample for infrared spectroscopy and normal mode analysis experiments in the physical chemistry laboratory. Students use HyperChem to calculate the vibrational spectrum and visualize vibrational motions; the infrared activities of the vibrational modes are then predicted using group theory. Because all fundamental, overtone, and combination bands of OCS are infrared active, the spectrum of OCS has many features for students to assign. The rotational substructure of the fundamental transitions is also partially resolved and can be explained in terms of the selection rules for parallel and perpendicular transitions. Finally, we describe the unique observation of a hot band transition in the infrared for the ν 2 bending mode and compare its intensity to the relative population predicted from the Boltzmann distribution.