Abstract: The discovery of a method and the invention of a system for obtaining very high selectivity—and dissociation of the desired 235UF6 isotope in the Molecular Laser Isotope Separation (MLIS) process of the Uranium Hexafluoride (UF6) isotopes, in a single highly selective step, is described. The principle of the process and the concept of the invention are very simple: At temperatures below 100° K., and. preferably in the region of 60° K, nearly all the molecules of the expansion supercooled UE6 gas are in the ground state enabling the principles of the invention to be practically applied without-any ‘interference from other inherent, processes. Then the frequency of the selecting laser must be at 628.527 cm?1, or very close to it, for a three-photon absorption resonance with the [m(A2):(3V3)] sublevel of the third energy excitation state of the desired 235UF6 isotope. The fixing of the frequency of the selecting laser is the first basic step of the invention.

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.