The dominating theory of olfaction is the shape theory which is based on the key-lock model. However, experiments have shown that matching of shape and size with odorant receptors are still insufficient to explain the mechanism of how human noses work. The strongest evidence is the isotope experiments. With the inelastic tunneling mechanism proposed by Luca Turin in 1996, we first study the vibration theory based on the phonon-assisted tunneling mechanism, and calculate tunneling rate using Fermi's golden rule. Then, we develop our algorithm to plot molecular spectra of vibration with y axis labeling the odors' coupling strength with odorant receptors. With these spectra, we can predict the existence of isotope effects of any kind of molecules, and provide more direct suggestions to experiments. All make a further step to the humans' understanding toward the ultimate theory of olfaction.

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