Structural study and vibrational analyses of the monomeric,dimeric,trimeric and tetrameric species of acetamide by using the FT-IR and Raman spectra,DFT calculations and SQM methodology

Structural and vibrational study of acetamide and its hydrogen bonded dimer,trimer and tetramers have been performed using dft/b3lyp method with 6-311++g(d,p) basis set. particular attention has been focused on the intermolecular n-h...o hydrogen bonding forming the acetamide species. natural bond orbital (nbo) analysis is performed in order to explore interactions and charge transfer among different orbitals and lone pairs taking place within the acetamide species. in addition,the atomic in molecule (aim) analysis is used to study the properties of the intermolecular hydrogen bonding in the acetamide complexes on the basis of topological parameters calculated at bond critical points. the dft calculations were combined with pulay's scaled quantum mechanics force field (sqmff) methodology to fit the calculated wavenumbers to the experimental ones. moreover,the red shifts of n-h and c=o stretching vibrational modes upon formation of the hydrogen bonded acetamide species have been discussed.