The mechanism of a reversible Xe transfer in the atomic switch is theoretically investigated. It is demonstrated that Xe transfer is caused by inelastic scattering from the tunneling electrons, leading to vibrational excitation in one of the potential well and transfer of it to the deeper well. The transfer rate, essentially determined by the vibrational excitation, has a power law dependence on the bias, where the power equals approximately the number of levels in the potential. The coupling to the electric field and the elastic scattering by the tunnelling electrons introduce a potential difference between the double well, which affects the direction of Xe transfer.