Electronic structure of 1,4-dihydro-1,2,4,5-tetrazines and of related 1,4-dihydroaromatic compounds. Journal of the Chemical Society, Perkin Transactions 2: Physical Organic Chemistry, 10:1633--1637, 1985. [PUMA: voltammetry tetrazine;cyclohexadiene MO configuration tetrazine;pyrazine MO;hexazine electron MO;MO azine;photoelectron spectra cyclic]