HILGERS, F., KAIM, W., SCHULZ, A., ZÁLIŠ, S. Electronic Absorption Spectroscopy of Some Exceptionally Stable 1,4-dialkyl-1,4-dihydro-1,4-diazinium Radical Cations: Assignment of Transitions, Vibrational Structure and Effects of Dimerization. Journal of the Chemical Society. Perkin Transactions II. 1994, č. 1, 135-138. ISSN 0300-9580.