New development in the studies of short-lived paramagnetic species by time-resolved ESR

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The purpose of this research is to extend our time-resolved ESR work further and to seek new developments. There are two directions for new developments. One is to develop new methodology and the other is to make new applications to interesting systems. in the first area we have tried CIDEP-ENDOR and delayed transient nutation techniques. We have completed preliminary experiments, but further investigations are needed to evaluate the full potential of these techniques. In the second area we have obtained the following results.1) Studies of short-lived triplet statesa) Intramolecularly hydrogen@bonded molecules ; We have investigated the triplet properties of methylsalicvlate and related molecules in mixed single crystals. The obtained results were examined in comparison with the result of an UHF MO calculation. Time-resolved ESR studies were made on the triplet states of benzoxazole and bezothiazole in various solvents to clarify their triplet properties.b) Pyridine derivatives ; The nature of the triplet state of 4-cyanopyridine was clarified from a n ESR study together with the results of phosphorescence studies and an ab initio calculation. It was found that the triplet state is of mixed 3npi^* and 3pipi^* character with a very distorted structure.c) Triplet states of C_6 and C_<70> ; A time-resolved ESR study revealed remarkable structural and dynamic properties of the triplet states of these molecules. Detailed studies are being made at present.2) Studies of short-lived radicals ; We have studied CIDEP of benzil in various solvents, particularly the polarization mechanisms and the processes responsible for producing the initial slow rise of the, CIDEP signals at low temperatures.