The resonant or near‐resonant interaction of two atoms or molecules, in states which can respectively emit and absorb photons of nearly the same energy, allows them to scatter with large cross sections compared to the usual van der Waals cross sections. This enhanced scattering can be used to separate a mixture of isotopes in a beam. In most cases, a laser or maser is needed to selectively excite the isotope of interest. For the separation of hydrogen and deuterium, however, a single‐step enrichment of nearly 30‐fold is calculated at 25% deuterium recovery without the use of lasers or masers.