Vibrational Assignment and Density Functional Theory Efficiency in Predicting the Vibrational Frequencies of Thiophenol

Theoretical calculations of the vibrational frequencies for polyatomic species have become an invaluable chemical tool over the past decade. This can be largely attributed to the increased availability and efficiency of robust energy derivative programs, in which the first and second derivatives are computed analytically [1], and the increased power of affordable computers. These advances have pushed the applicability of first-principle investigation of molecular vibrational properties from the small molecule domain to the treatment of reasonably large systems [2-6]. In the field of computational vibrational spectroscopy of molecules [7,8] the late 20th and early 21th century were marked by switching the attention from conventional solution of the inverse vibrational problem (IVP) to prediction of vibrational frequencies of molecules and the intensities of spectral bands by means of quantummechanical calculation methods such as the Hartree-Fock method (HF) [9], Möller-Plesset (MP) perturbation theory [9], and density functional theory (DFT) [10,11]. However, to reach the best fit to the observed vibration frequencies, the values of the force fields obtained by these methods need certain empirical corrections. The aim of this work is obtaining the performance of the most common quantum chemical methods in calculating the vibrational frequencies of TP, which to the best of our knowledge has not been appeared in literature. To compare the calculated results with the experimental, the FT-IR and FT-Raman spectra of TP were also recorded in the 100-3500 cm^-1 region.