Vibrational spectra, nonlinear optical properties, NBO analysis and thermodynamic properties of N-phenylethanolamine by density functional method

In the present work, we reported a combined experimental and theoretical study on molecular structure and vibrational analysis of N-phenylethanolamine (NPEA). FT-IR and FT-Raman spectra of the title compound in the solid phase are recorded in the region 4000–400 cm and 3500–100 cm, respectively. The structural and spectroscopic data of the molecule in the ground state is calculated using density functional method with LSDA/6311+G(d,p) and B3PW91/6-311+G(d,p) levels. The DFT (B3PW91/6-311+G(d,p)) calculations have been giving energies, optimized structures, harmonic vibrational frequencies, IR intensities and Raman activities. The study is extended to the HOMO–LUMO analysis to calculate the energy gap, ionization potential, electron affinity, global hardness, chemical potential and thermodynamic properties of NPEA. The calculated HOMO and LUMO energies show the charge transfer occurs in the molecule. A complete vibrational assignment aided by the theoretical harmonic frequency analysis has been proposed. The harmonic vibrational frequencies have been compared experimental FT-IR and FT-Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete vibrational assignments are performed on the basis of the total energy distribution (TED) of the vibrational modes calculated with scaled quantum mechanical (SQM) method.