We obtain infrared spectra of each isotopologue of propionate, in the gas phase and from 25 snapshots in the MD trajectory, each 20 ns apart. We estimate the effect of the protein environment on the infrared spectra by averaging the wavenumber ν (in cm -1 ) of each vibrational peak and its infrared intensity (in arbitrary units) over the twenty-five spectral snapshots. Because the peaks are so far apart in time, we assume that their residuals are independent of one another, and model their thermal fluctuations as the standard deviation of the frequencies. We visualize these standard deviations as the width of each peak's Gaussian distribution. Time-averaged spectra of all 32 isotopologues are available in the Supplemental Material; the underlying data and scripts used to generate the spectra are available in the Duke Research Data Repository .