Electronic Structure of Thymine

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Abstract
The electronic structures of the ground and low‐lying excited states of thymine and the anions 1‐HT− and 3‐HT−, derived by removing a proton from nitrogen atom N3 and N1, respectively, have been described by all‐electron all‐integral LCAO–SCF calculations using Gaussian basis functions. In accord with experiment, we find the carbonyl bonds weakened in the anions relative to thymine because of a decrease in their overlap charge densities. On the other hand, our calculations and interpretation of the observed optical and ESR spectra suggest that both for T and 1‐HT− the lowest singlet and triplet π → π* states are very similar and localized in the region of the ethylenic bond of thymine.