X-ray scattering and density-functional theory calculations to study the presence of hydrogen-bonded clusters in liquid N-methylacetamide

A structural investigation of liquid N-methylacetamide (NMA) is performed by x-ray scattering and density functional theory (DFT). Experimental data are analyzed to yield the total structure function SM(Q) and the pair correlation function g(r). The DFT calculations, using the standard triple zeta valence basis set augmented by a diffuse function for carbon, nitrogen and oxygen atoms, are performed on the one hand to study the structure and stability of the two possible conformers cis and trans. On the other hand, they are meant to examine some possible clusters which may describe the intermolecular arrangement in liquid NMA. Among two series of dimers and trimers associations, the spectra are particularly interpreted in terms of: Trans NMA dimers and trimers which resemble the short-range crystal structure, mixed cis and trans trimers and cis cyclic trimers. The H-bonding parameters and the intermolecular energy for each model are described.