Isotope separation using the effect of resonant microwaves on the rate of triplet state photochemistry in solids

The rate of solid state photochemistry of excited triplet molecules at low temperatures, when the spin-lattice relaxation between the zero-field (zf) spin levels is slow, can be altered by exposing the excited sample to microwave radiation in resonance with its zf transitions. Triplet molecules with atoms having a nuclear spin, I greater than /sup 1///sub 2/, normally show hyperfine lines resulting from electron-nuclear spin transitions, a set for each isotope in the isotopic mixture. The irradiation with microwaves having a frequency corresponding to only one isotope can change the rate of photochemistry of its triplet molecules from that for the molecules containing the other isotopes in the sample. This leads to preferential photochemical destruction of molecules containing one isotope over the other(s). This technique is proposed for separating N, Cl, Br, B (and maybe U) isotopes and an expression is derived relating the isotope separation factor to characteristic pumping and decay rate constants of the reacting triplet molecules.