For strong tunnelling to be possible, the odorant molecule must first fit in the receptor's binding site, and then it must have a vibrational energy mode compatible with the difference in energies between the two energy levels on the receptor.
The odorant molecule must first fit in the receptor's binding site. This is for strong tunnelling. This is to be possible. It must have a vibrational energy mode compatible with the difference in energies between the two energy levels on the receptor. This is then. This is for strong tunnelling. This is to be possible.