Optical and Magnetic Field Studies of the Lowest Triplet State of the Pyrazine Crystal

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Abstract
The electronic absorptionspectrum of pyrazine crystals has been studied using single crystals at 4.2°K and polarized light. The origin shows three lines that are interpreted as (i) a B 3u + , k = 0, factor group state at 26247.6 cm−1, (ii) two lines at 26254.7 and 26253.4 cm−1 corresponding to a split B 2u − , k = 0 , factor group state. These interpretations are made on the basis of high‐field Zeeman effect studies. A low‐field Zeeman study has revealed the ordering of magnetic substates in each factor group level at T c < T b < T a . This yields the order T y < T z < T x for the free molecule. The zero‐field splitting is approximately + 0.3 cm−1 (D = − 3 2 Y) . A discussion of the relationship between such spin‐state ordering and the electronic structure of pyrazine in a 3 n + π 4 *(nπ bb ) state is also presented.