Educational Applications of Infrared and Raman Spectroscopy: A Comparison of Experiment and Theory

Advances in Raman spectroscopy and computer technology facilitate the introduction of current spectroscopic and molecular modeling methods at the undergraduate level. This study compares experimental infrared (IR) and Raman spectra of selected molecules to calculated spectra using semiempirical and ab initio methods. These illustrate the complimentary nature of IR and Raman spectroscopies as well as the limitation and successes of computational methods in predicting molecular vibrational frequencies and intensities. Particular examples used to illustrate these principles include comparisons of cis- and trans-1,2-dichloroethene as well as methanol and d1-methanol. The former comparison illustrates symmetry selection rules, and the latter demonstrates the use of isotopic substitution in the assignment of vibrational spectra.