Knowledge Bank

Protonated water clusters have been the focus of theoretical interest for two decades, but few results on their spectra have been reported so $fara$. Research on neutral water clusters in the last few years has shown that a pulsed supersonic slit expansion source allows observation of spectra up to the $hexamerb$. Because of the stronger ion-dipole interaction and the expected higher binding energy of protonated water clusters (30 kcal/mol H2O), these might also be observable by using a pulsed slit source with a high current (high ionization degree) $dischargec$. We present very dense THz laser absorption spectra obtained with a $NeHe/D2O$-operated discharge expansion in the range of 1000-2500 GHz $(30-75cm-1)$, using an advanced pulsed discharge slit source. We present assignments of lines of the species OD, $D2O+$ and $D3O+$ and their hot band rotational lines, and discuss progress in assigning the many unassigned features.