Knowledge Bank

We have measured the far-infrared vibration-rotation-tunneling (VRT) spectrum of an intermolecular vibration of $(D2O)2$ near $68cm-1$. In addition, further transitions of the VRT band of $(D2O)2$ previously reported by $Puglianoetal1$ have been observed. By considering symmetry restraints on the selection rules, these bands have been assigned to the out-of-plane H-bond torsional and in-plane acceptor waggins modes predicted by many theoretical $calculations2.$ The experimental-theoretical discrepancy in the measured frequencies of these bands indicates the importance of a fully coupled six-dimmensional calculation of the dynamics for the water dimer.