Method for separating krypton isotopes

A method for separating krypton 85 from a mixture of a plurality of krypton isotopes including .sup.83 Kr, .sup.84 Kr, .sup.85 Kr, and .sup.86 Kr, comprising

• reacting the mixture of krypton isotopes with fluorine to provide a thermodynamically unstable mixed isotope krypton difluoride source material which spontaneously decomposes on an isotopically non-selective basis,
• maintaining said mixed isotope krypton difluoride source material at a low temperature of less than about 0.degree. C. while selectively irradiating said mixed isotope krypton difluoride source material with infrared radiation at a wavelength at a frequency selected from the asymmetric stretching frequency of the .sup.85 KrF.sub.2 molecule at 586.7 cm.sup.-1, the .nu..sub.2 vibrational frequency of the .sup.85 KrF.sub.2 molecule at 233 cm.sup.-1, the .nu..sub.3 vibrational frequency of the .sup.85 KrF.sub.2 molecule at 558 cm.sup.-1 or the .nu..sub.1 +.nu..sub.3 combination vibrational frequency of the .sup.85 KrF.sub.2 molecule at 1032 cm.sup.-1 which frequency is selectively absorbed by .sup.85 krypton difluoride and decomposing the selectively excited .sup.85 krypton difluoride compound to .sup.85 krypton and fluorine, and
• separating the decomposition product .sup.85 krypton from the fluorine and remaining undecomposed krypton difluoride source material.