EPR and ENDOR of triplet state diphenyl-h10 in diphenyl-d10 single crystals. Structural implications

The results of EPR and ENDOR spectroscopic measurements for the lowest energy triplet state of diphenyl-h10 molecules dilutely substituted for host molecules in diphenyl-d10 single crystals at 1.9 °K are reported. Our data indicate that the triplet state diphenyl-h10 molecules do not possess inversion symmetry but that any concomitant deviation from zero for the value of the angle between the normals to the mean planes of the two phenyl groups is necessarily less than 0.008π (1.5°). We present a discussion of this result in the light of recent results concerning the low temperature structure of the diphenyl crystal.