ANOMALOUS MAGNETIC-FIELD EFFECTS OBSERVED IN THE REACTION OF A TRIPLET BIRADICAL INVOLVING AN O-CENTERED RADICAL

The hydrogen abstraction of a benzophenone-phenol chain-linked compoun d was investigated in acetonitrile by means of a nanosecond laser flas h photolysis technique at magnetic fields of 0-1.7 T. The Lifetime and the initial yield of a triplet biradical involving the benzophenone k etyl and phenoxyl radicals decreased with increasing magnetic field st rength (B) from 0 to 0.005 T, but it increased with increasing B from 0.005 to 0.2 T. In a high-field region (0.2 T < B less than or equal t o 1.7 T), the lifetime did not change appreciably, but the initial yie ld of the biradical decreased with increasing B. These anomalous magne tic field effects may be interpreted by the level-crossing mechanism a t the low-field region and the Delta g mechanism at the high-field one .