Molecular structure and vibrational spectra of 4-phenylsemicarbazide by density functional method

In this paper, combined experimental and theoretical study on molecular and vibrational structure of 4-phenylsemicarbazide (4PSC) were reported. The Fourier transform infrared (FT-IR) spectrum of 4PSC was recorded in the region 4000–400 cm−1. Fourier transform Raman (FT-Raman) spectrum of 4PSC was also recorded in the region 3500–50 cm−1. Semi-empirical PM3 method was used for conformational distribution of possible conformers. The molecular geometry and vibrational frequencies of the most stable conformer of 4PSC in the ground state have been calculated by using the density functional BLYP and B3LYP methods with 6-31G(d) and 6-31G(d,p) as basis sets. The optimized geometrical parameters obtained from theoretical calculations show good agreement with the XRD experimental values. The ground state energies, dipole moments and thermodynamic parameters have also been computed. The calculated and scaled frequencies were compared with experimental values and on the basis of this comparison and PED data assignments of fundamental vibrational modes were examined. The differences between the observed and BLYP/6-31G(d) scaled wavenumber values of most of the fundamentals are very small.