A complete vibrational analysis of the methyl ammonium ion CH3NH3+, and of CD3NH3+, CH3ND3+ and CD3ND3+ is described in this paper. A General valence Force Field has been computed for these ions, belonging to C3ν sysmmetry, using the fundamental frequencies obtained from the infrared spectra. The mean square amplitudes and shrinkage constants and Coriolis coupling constants have also been calculated for the first time and presented here.
