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.