Light - induced conversion of nuclear spin isomers of molecules

We report on a new phenomenon of molecular nuclear spin isomers conversion in the field of resonant laser radiation. It is based on the isomer-selective optical excitation and the difference of conversion rates for excited and unexcited molecules. We expect the considerable magnitude of the effect for all molecules which absorb the radiation of existing lasers. In a recent work [1] a phenomenon of enrichment of nuclear spin isomers of molecules was predicted. The enrichment appears in the course of selective laser excitation of definite spin isomers. It was expected that the proposed enrichment method was the most applicable to the molecules where the nuclear spin conversion was induced by intramolecular spin-state mixing interaction. As it was shown in [1], the enrichment could be very high under an appropriate frequency of excited radiation. On the other hand, there were strict limitations placed on the laser frequency. In particular, the abilities of CO 2-laser and other sources appear to be insufficient for CH 3 F molecule, which is other than that a very convenient object for investigation of the enrichment phenomenon. The efficiently absorbed lines of CO 2-laser in CH 3 F do not satisfy the conditions from [1]. Thus the realization of the idea [1] is uneasy due to problems with compatible object and radiation source finding. As it turns out the frequency constraints from [1] may be removed without any considerable loss of enrichment. There stays only one condition for the frequency to meet: The radiation should effectively be absorbed on a vibrational or electronic transition from the molecule ground state. This indulgence radically expands the set of relevant objects (those, demonstrating the light-induced conversion with available radiation sources). The physical nature of the proposed phenomenon is quite similar to that of light-induced drift (LID) [2] 1 and other light-induced gas-kinetic effects (see, e.g., [4]). Their common essence is in the following: if radiation excites particles selectively with respect to a physical parameter, than the difference of rates of relaxation of the parameter for excited and unexcited particles shifts the mean stationary value of the parameter from the equilibrium.