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SUSANA BLANCO, ALBERTO LESARRI, JUAN C. LÓPEZ AND JOSÉ L. ALONSO, Grupo de Espectroscopía Molecular (GEM), Departamento de Química Física y Química Inorgánica, Facultad de Ciencias, Universidad de Valladolid, E-47005 Valladolid, Spain.
Formamide (NH2-COH) is the most simple molecule carrying the peptide linkage and its microsolvated clusters can be used to investigate the diverse hydrogen bond interactions of water with this functional group. A molecular beam Fourier Transform microwave spectrometer\footnote ~J. L. Alonso, F. Lorenzo, J. C. López, A. Lesarri, S. Mata and H. Dreizler; Chem. Phys. , \textbf218, 267 (1997) equipped with a heating nozzle\footnote ~S. Blanco, J. C. López, J. L. Alonso, P. Ottaviani and W. Caminati; J. Chem. Phys. , \textbf119, 880 (2003) has been used for this research. The most stable conformer of the formamide-H2O complex, previously observed by Lovas et al. , is stabilized by two hydrogen bonds O-H
O=C and N-H
O with water closing a cycle with the peptide functional group. In the present work we have observed two new formamide-H2O conformers and the trimer formamide-(H2O)2. In the second most stable 1:1 conformer water is placed on the other side of the carbonyl group stabilized by a O-H
O=C hydrogen bond and by a C-H
O weak hydrogen bond. In the third 1:1 complex, water is bonded to the amino group by a N-H
O hydrogen bond. For the formamide-(H2O)2 complex the two molecules of water close a cycle with the peptide group with three different hydrogen bonds (O-H
O=C, O-H
O and N-H
O). The rotational spectra of the parent and several D/H, 15N/14N, 13C/12C and 18O/16O isotopically substituted species have been measured for the formamide monomer, the most stable conformer of the formamide-H2O adduct and the formamide-(H2O)2 complex in order to investigate their structures. High level ab initio computations have been performed in order to complement the experimental results.