Since we compute IR spectra in the harmonic approximation, the geometry, Hessian, and dipole moments are all independent of isotopic composition. Thus, they are obtained only for the all-H isotopologue C 2 H 5 COO -. We then weight them by the nuclear masses of each of the 32 isotopologues to obtain its vibrational frequencies and IR intensities without requiring a repetition of the full calculation; this feature is available in the NEW branch of ASH. We additionally compute the infrared spectra of each isotopologue of propionate in the gas phase under the same computational workflow (except for QM/MM embedding).