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 p-p dimerization. Journal of the Chemical Society, Perkin Transactions 2: Physical Organic Chemistry, 1:135--138, 1994. [PUMA: UV absorption cation cation;transition cation;vibrational dialkyldihydrodiazinium dimerization electronic pi radical stable structure]