Abstract: A simple system for obtaining high dissociation yield in a single highly selective step, even at very high pumping powers, in the molecular laser isotope separation (MLIS) route of Uranium Hexafluoride (UF.sub.6), is described. In order to selectively excite and dissociate the desired isotope .sup.235 UF.sub.6 two beams with frequencies corresponding to the first and second energy excitation levels of this isotope at .omega..sub.1 =.omega..sub.0 and .omega..sub.2 =.omega..sub.0 +.omega..sub.12 respectively where .omega..sub.12 is the frequency difference between the first and second energy excitation levels, are simultaneously applied to the supercooled Uranium Hexafluoride molecular gas.