Laser isotope separation by multiple photon absorption

It has been discovered that infrared laser radiation of sufficient intensity and of a frequency which selectively excites only molecules containing a particular isotope may readily produce multiple photon absorption in molecules having a sufficient density of vibrational states. Multiple photon absorption may be used to produce an excited vibrational state in the excited molecules at which chemical reaction occurs, or an excited vibrational state at which a more advantageous frequency of a second laser may be used to produce selective chemical reacton in a two step process. To minimize collisional scrambling effects, it is essential that the molecular species being irradiated be present in a dilute fluid; a gas is preferred. In one embodiment of the invention, multiple photon absorption of infrared photons results in an excited state at which the selectively excited molecules undergo chemical reaction with a second chemical species present in admixture with these molecules. In another embodiment, the multiple photon absorption results in a dissociation of the selectively excited molecules. In a third embodiment, the multiple photon absorption results in dissocation of the selectively excited molecules with at least one of the dissociation products undergoing rapid chemical reacton with a second chemical species present in the irradiated fluid. The CO2 laser is particularly well suited for use with the method of this invention in that there are CO2 lines which coincide with spectral features of the volatile halides of many elements. Examples of such halides include SF6, SiF4, CH3F, BCl3, NF3 and CF2Cl2. Because hydrogen reacts rapidly wth halogens, CO2 laser irradiation of admixtures of such volatle halides with hydrogen is a particularly advantageous way to produce selective chemical reaction in the method of the invention. (LL)