bending and the umbrella motion in NH 3 (see Fig. for comparison), which is now coupled to the bending motion in the fragment CH 3 as well as to the vibration of the CH bond that is not involved in CH 3 . We confirm here, as seen in Fig. , that vibrations in NH 3 cannot be completely decoupled from those in other fragments, probably due to strong anharmonicity. This is further supported by the lack of full localization of the corresponding absorption bands, which remain delocalized and present several peaks. The three remaining bands are located in