Spectral origins and ionization potentials of guanine tautomers: Theoretical elucidation of experimental findings

The HF, B3LYP, MP2, TDDFT and CIS methods along with the 6-311G(d,p) and 6-311++G(d,p) basis sets have been used to compute the relative stability, ionization potentials, lowest singlet ππ∗ vertical transition energy and the corresponding spectral origins of the 28 guanine tautomers. Significant variations in the ionization potentials and spectral origins among guanine tautomers were revealed. We believe that the computed results would be helpful to interpret the complex R2PI spectra of guanine obtained in the supersonic jet-beam experiments.