The temperature dependent Raman spectra of the title compound confirm the presence of some rotational disorder of the NH3 end groups below 112 K. The central carbon-carbon stretching mode around 865 cm-1 is coupled to the order parameter of the incommensurate phase transition at 168 K. No other clear evidence of the incommensurate modulation appears in the Raman spectra between 112 and 168 K. In the Abma phase (above 168 K) a dynamic conformational gauche-trans equilibrium is observed. The corresponding enthalpy difference is estimated to be 18.4+or-6.5 kJ mol-1.