Theoretical study of the spectroscopy of methyl substituted 2-Pyridones, tautomers and ions

We present an extended study on the structure and the properties of the low lying electronic states of methyl substituted 2-Pyridone, of their tautomers and of their positively charged ions. We performed these calculations using density functional theory method (PBE0 DFT) and the complete active space self consistent field (CASSCF) approach in connection with the aug-cc-pVDZ and aug-cc-pVTZ Dunning’s basis sets. Our results include their equilibrium geometries, their rotational and vibrational spectroscopic parameters, their vertical excitation spectra and their vertical and adiabatic ionization energies. The role of substitution by the methyl on the electronic structure, on the spectroscopy of the 2-Pyridone/2-Hydroxypyridine and on the tautomerism is examined. The lowest electronic excited states of these systems are found to lay relatively close in energy, which should favor their couplings and the mixing of their electronic wavefunctions.