Appl. Magn. Reson. 9, 355-365 (1995) Applied Magnetic Resonance 9 Springe~Verlag 1995 Printed in Austria CIDNP in Photolysis of Acetone Solutions in Plastic Crystals of Cyclohexane-d12 A. A. Obynochny ~, P.A. Purtov ~, A. G. Maryasov 1, Y. N. Molin 1, K. M. Salikhov 2, and E. D. Skakovsky 3 ~Institute of Chemical Kinetics and Combustion, Novosibirsk, Russian Federation 2Zavoisky Physical-Technical Institute, Kazan, Russian Federation 3Institute of Physical-Organical Chemistry, Minsk, Byelorussia Received June 2, 1995 Abstract. The emissive CIDNP was observed during photolysis of acetone solutions in solid cyclo- hexane-d~2. The polarization is assumed to arise in contact triplet radical pairs asa result of their T -S, conversion and their recombination. 1. Introduction The chemically induced dynamic nuclear polarization (CIDNP) arises in liquid- phase radical reactions in strong magnetic fields mainly due to S-T 0 evolution of radical pairs (e.g., [1, 2]). The evolution occurs at relatively large inter radi- cal separation, where the exchange interaction between radicals is negligible. In solids, as compared to liquids, the diffusion mobility of radicals is either com- pletely frozen or slowed down. In solid organic substances in the reactions of photodissociation and photoabstraction, the radicals are formed in the immediate vicinity of each other and are able to recombine (disproportionate) without es- caping into the bulk. The S-T 0 mechanism of CIDNP is ineffective in this case because the radicals are located in a region of strong exchange interaction. How- ever, the favourable conditions can appear for observing the other mechanisms of CIDNP formation. These include: (i) the S-T_ (S-T+) mechanism of net elec- tron and nuclear polarization; (ii) the triplet mechanism (TM) of electron polar- ization with subsequent polarization transfer to the nuclear subsystem due to cross-relaxation (e.g., [3, 4]). One of the problems of observation of CIDNP in solid organic substances is associated with a substantial broadening of NMR lines. This problem can be