Investigation of aniline by high pressure Raman scattering spectroscopy and quantum chemical calculation

The unexpected redshifts of the NH and the blueshifts of the CH stretching frequencies with increasing pressure were observed in the pressure dependent Raman spectra of aniline at 0−7.7 GPa. Based on the natural bond orbital (NBO) analysis, the opposite frequency shifts of the CH and NH vibrations are attributed to the different pressure-induced change in the electronic antibonding occupancies of NH and CH. Further, the antibonding occupancy of \hbox{$\pi_{\mathrm{C{\mbox{-}}C}}^{\ast}$} π C - C ∗ and the charge of phenyl ring in aniline were evaluated, characterizing an increase of antibonding occupancy of \hbox{$\pi ^{\ast}_{\mathrm{C\mbox{-}C}}$} π C - C ∗ and a decrease of phenyl ring’s charge with increasing pressure. These results reflect that the NH-π and CH-π bonds, as the research target of intermolecular interaction, are becoming weaker as the pressure increases. The research would improve the understanding of the pressure effect on the intermolecular interactions of aniline.