Infrared Spectra Of The Methylamine Dimer And Methylamine-water Complexes In Solid Neon Between 80 And 5500 <span Class="roman">cm</span>^&#8722;1

For the first time the investigation of water molecule complexed with methylamine (\chem{CH_3 NH_2}) in solid neon was performed from the far to the near infrared using FTIR spectroscopy. By comparison with other hydrogen-bonded complexes and with the help of theoretical results we have identify several vibrational transitions for \chem{CH_3 NH_2} dimer, \chem{CH_3 NH_2}-\chem{H_2O}, and \chem{CH_3 NH_2}–(\chem{H_2O})$_{2}$ complexes. Theoretical calculations at the MP2 level have been performed to obtain their equilibrium geometries and vibrational spectra at the harmonic level and comparison with experimental data allows us to give structures of observed complexes. For the \chem{CH_3 NH_2}-\chem{H_2O} complex, the infrared spectral changes (frequencies as well as intensities) indicate that the water plays the role of the proton donor, in agreement with the previous theoretical works. Careful examination of the far infrared allows the assignment of several intermolecular modes, confirmed by the observation of combinations of intra+intermolecular transitions. All of these results significantly increase the number of one and, especially, two quanta vibrational transitions for these complexes. This study shows the high sensibility of the solid neon isolation to the spectroscopy of the hydrogen-bonded complexes since two quanta transitions can’t be easily observed in gas phase