In this work, we present the first computational infrared spectra of an olfactant molecule bound to an OR, including all its possible isotopologues. The high-frequency vibrational modes, above 2000 cm -1 , of the olfactant in its binding site, differ based on isotopic composition. This difference is large relative both to the variance in the modes due to thermal noise and to the thermal energy available under physiological conditions. We do not address a specific mechanism by which vibrations couple to the OR. Indeed, the unprecedented structural detail observed by Billesbølle et al. demonstrates that noncovalent bonds to the ligand and the shape of the binding pocket play integral roles in olfactant recognition. However, we keep open a door for the impact of vibrational modes to be felt-that is, smelt-by the high-energy vibrations of olfactant molecules.