Heterionic vibrational coupling in crystalline methylammonium nitrate
Abstract
Heterionic vibrational coupling is shown to exist between the CH3 and NH3 deformation modes of the monomethylammonium cation and the antisymmetric stretching mode, ν(N—O), of the nitrate anion in the salt monomethylammonium nitrate in the solid state. It is concluded that neither a dipole–dipole nor a hydrogen-bonding mechanism separately provides an adequate explanation of these couplings. A clear relationship between the spectra and crystal pseudosymmetry is also shown to exist.