Comparison of DFT calculated and measured IR absorption spectra

Identification of target molecules, based on spectrum-feature extraction by comparison of spectra, can be accomplished using signal templates having patterns associated with known materials. This study examines the concept of using IR spectra calculated using density functional theory (DFT) as signal templates. In principle, DFT calculated IR spectra should provide reasonable templates for comparison with IR spectral measurements associated with different types of detector schemes and complex spectral-signature backgrounds. In practice, however, there exists artifacts due to computational errors and model assumptions in the case of DFT calculated spectra, and artifacts due to measurement errors and experimental-design assumptions in the case of spectral measurements. Accordingly, the use of DFT calculated spectra as signal templates must consider these artifacts. In this study, case-study analysis of IR absorption spectra for a water contaminant of interest is presented, which demonstrates aspects of using DFT calculated IR spectra to determine the presence of target molecules.