Abstract: A process and apparatus for separating isotopes from gaseous mixtures by forming a seeded molecular beam comprising a carrier gas and the isotopes, exposing the seeded beam to a laser light having a particular radiation frequency to accentuate differences in the velocity profiles of the isotopes in the beam and separating the isotopes based upon the differences in their velocity profiles. The frequency of the laser is such as to excite only one of the isotopes, e.g. the lighter one, so that it possesses a larger amount of rotational energy without exciting the other isotope(s).