Stark effects on the B 1g and A u nπ* triplet states of p-benzoquinone

Abstract

The results of polarized Stark effect absorption experiments on the lower triplet states of p-benzoquinone (PBQ)- h 4 and - d 4 in single crystals at 1.8°K are reported. These measurements give strong support for the assignment of the lowest triplet state as triplet 3B 1g (nπ*). The origin of this state in PBQ- h 4 is observed as an electric field induced transition at 18602.8 cm −1 and is interpreted as the g-inversion level of a double-minimum potential well. The line observed at 18619.7 cm −1 in the PBQ- h 4 crystal is therefore assigned as the u-inversion level of this double well with A u (B 1g Θ b 1u) total symmetry. Its intensity manifests the strong vibronic coupling that occurs among the B tg and A u nπ* triplet states along b 1u-type nuclear motions.