Knowledge Bank

Two new intermolecular vibrations of $(NH3)2$ have been observed by tunable for infrared laser spectroscopy in a planar jet. So far, 288 absorption lines between 80 and $90cm-1$ have been assigned to 32 subbands of the two vibrations. One vibration has b-type (out-of-plane) selection rules and is assigned as a torsion about the intermolecular bond axis. The other has a-type (in-plane) selection rules and is tentatively assigned as the geared’ in-plane bend, or equivalently, the second overtone of donor’ - `acceptor’ interchange. The vibrational assignments of the new spectra and the proton tunneling dynamics in the excited states will be discussed.