Ab initio Study of the Hydrogen-bonded Clusters of N-methylformamide-water

The N-methylformamide（NMF）-water clusters were studied by ab inito calculations at MP2/6-31+G** and MP2 / 6-311 ++ G（d，p）levels. The equilibrium geometries and the dissociation channels and dissociation energies of both neutral and ionic NMF-H2O clusters are presented. For N-methylformamide，cis-form has lower energy than trans-form. In NMFH+，the proton prefers to link with the O atom of N-methylformamide. The results show that both cis- and trans- form of NMF can form a linear hydrogen bond with water. Although the energy of trans-NMF is higher than cis-NMF，trans-form exits more stably because it can form a double hydrogen bond with water. After the ionization of the NMF-H2O cluster，both the cis- and the trans-form will produce protonated products.