Light-induced conversion of nuclear spin modifications of molecules

We report a new effect in which one nuclear spin modification of molecules is converted into another in a resonance laser radiation field. The effect is based on selective (with respect to modifications) optical excitation an d the difference of the conversion rates of spin modifications for excited and unexcited molecules. The effect is expected to be very substantial and should occur for all molecules capable of absorbing the radiation of existi ng lasers. (C) 1999 American Institute of Physics. [S0021-3640(99)00420-X].