Molecular structure and vibrational IR spectra of the [formula omitted] system and its thio and seleno analogs: density functional theory versus conventional ab initio calculations

Abstract

The molecular parameters (optimized geometries, rotational constants, dipole moments) and vibrational IR spectra (harmonic wavenumbers, absolute intensities) of the 2- hydroxypyridine 2(1H)- pyridinone ( 2 OHP 2 OP ) system and its thio ( 2 SHP 2 SP ) and seleno analogs ( 2 SeHP 2 SeP ) are predicted by density functional theory (DFT) with the Becke3-LYP functionals (DFT(B3-LYP) method) using a valence split double-ζ basis set augmented by polarization functions on all atoms. The results are compared with available experimental data and with the data calculated at the conventional ab initio (Hartree-Fock, MP2) levels. Molecular parameters (rotational constants, dipole moments) of 2-oxopyridine tautomers predicted by the DFT(B3-LYP) method agree well with recent gas-phase microwave data and with the parameters pedicted by the MP2 calculations. The vibrational IR spectra of the tautomers calculated by the DFT(B3-LYP) method agree much better with the recorded experimental spectra than the spectra predicted at the Hartree-Fock level and are also better than those predicted at the MP2 level. The DFT(B3-LYP) results for 2-thiopyridine tautomers are of a similar accuracy. The relative internal energies at 0K of the tautomeric species seem to be better predicted by conventional ab initio calculations than by the DFT(B3-LYP) method.