MOLECULAR STRUCTURE AND VIBRATIONAL SPECTRA OF THYMINE USING Ab-Initio AND DENSITY FUNCTIONAL THEORY

This work deals with theoretical and experimental study of vibrational spectra of thymine. The geometrical parameters (bond lengths and bond angles), harmonic vibrational frequencies, infrared intensities and Raman scattering activities have been calculated using ab- initio MP2 (second-order Møller–Plesset perturbation theory) method and the density functional B3LYP (Becke three-parameter hybrid functional combined with Lee–Yang–Parr correlation functional), X3LYP (extended hybrid functional combined with Lee–Yang–Parr correlation functional) and B3PW91 (Becke three-parameter hybrid functional combined with Perdew-Wang correlation functional) methods employing 6-311++G(d,p) as the basis set. The FTIR (Fourier-transform infrared spectroscopy) of the thymine in the range 400–4000 cm−1 in the solid phase has been recorded. A detailed interpretation of the infrared spectra of thymine has been reported. The theoretical optimized geometry parameters and wave numbers are in good agreement with the corresponding experimental values and with results found in most of the literature in most of cases without scaling.