Analysis of the rotational fine structure of the fundamental infrared band of HCl is a standard experiment in the physical chemistry laboratory curriculum. Although the absorption band was observed by Ångstrom and Palmer as early as 1893, the first spectrum showing sufficient resolution to distinguish not only the <i>P</i> and <i>R</i> branches but also the rotational fine structure was acquired in 1919 by Elmer S. Imes, the second African American to obtain a Ph.D. in physics. This spectrum, together with those obtained by Imes for HF and HBr, was of fundamental importance in demonstrating the need for a correct quantum theory of molecules. In celebration of the recent centenary of this spectrum, a number of extensions of the spectroscopy of the hydrogen halides beyond the standard curriculum are described here, including use of the research tool PGOPHER to facilitate data analysis, use of high-resolution linelist data from the HITRAN database to investigate overtones and hot bands, estimation of the bond dissociation energy from HITRAN data using Birge-Sponer extrapolation, and simulation of rovibrational bands based on high-level calculations of the ground state potential energy curve.

Using PGOPHER and HITRAN to extend spectroscopic analysis of hydrogen halides in the undergraduate laboratory

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