Etude des spectres de vibration et analyse en coordonnées normales des oxydes de triméthylamme, triméthylphosphine et triméthylarsine

Raman spectroscopic signatures of noncovalent interactions between trimethylamine N-oxide (TMAO) and water

The effects of hydration on vibrational normal modes of trimethylamine N-oxide (TMAO) are investigated by Raman spectroscopy and electronic structure computations. Microsolvated networks of water are observed to induce either red or blue shifts in the normal modes of TMAO with increasing water concentration and to also exhibit distinct spectral signatures. By taking advantage of the selective and gradual nature of the water-induced shifts and using comparisons to theoretical predictions, the assignments of TMAO's normal modes are re-examined and the structure of the hydrogen-bonded network in the vicinity of TMAO is elucidated. Agreement between experiment and theory suggests that the oxygen atom in TMAO accepts on average at least three hydrogen bonds from neighboring water molecules and that water molecules are likely not directly interacting with TMAO's methyl groups.

Vibrational frequencies and structural determination of trimethylarsine oxide

The normal mode frequencies and corresponding vibrational assignments of trimethylarsine oxide are examined theoretically using the Gaussian 98 set of quantum chemistry codes. All normal modes were successfully assigned to one of eight types of motion (As-C stretch, As=O stretch, C-H stretch, C-As-C bend, As=O bend, H-C-H bend, CH3 wag, and CH3 twist) utilizing the C3v symmetry of the molecule. Calculations were performed at the Hartree-Fock, DFT(B3LYP), and MP2 levels of theory using the standard 6-311G** basis. Calculated infrared intensities and Raman activities are reported.