THE SEARCH FOR PROTONATED WATER CLUSTERS: THZ LASER SPECTRUM OF A PULSED SUPERSONIC SLIT DISCHARGE: $D_{2}O^{+}, D_{3}O^{+}$, OD

$^{a}$L. I. Yeh, Y.T. Lee, J.T. Hougen $^{b}$K. Liu, M.G. Brown, R.J. Saykally, J. Phys. Chem. A, 1997, 101, 8995; K. Liu, M.G. Brown, J.D. Cruzan, R.J. Saykally, J. Phys. Chem. A. 1997, 101, 9011; J.D. Cruzan, M.R. Viant, M.G. Brown, R.J. Saykally, J. Phys. Chem. A, 1997, 101, 9022; M.R. Viant, J.D. Cruzan, D.D. Lucas, M.G. Brown, and others. J. Phys. Chem. A, 1997, 101, 9032. $^{c}$D.T. Anderson, S. Davis, T.S. Zwier, D.J. NesbittAuthor Institution: Department of Chemistry, University of California Berkeley, Berkeley, CA; Physical and Theoretical Chemical Laboratory, South Parks Road, Oxford, UKProtonated water clusters have been the focus of theoretical interest for two decades, but few results on their spectra have been reported so $far^{a}$. 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 $hexamer^{b}$. 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) $discharge^{c}$. We present very dense THz laser absorption spectra obtained with a $NeHe/D_{2}O$-operated discharge expansion in the range of 1000-2500 GHz $(30-75 cm^{-1})$, using an advanced pulsed discharge slit source. We present assignments of lines of the species OD, $D_{2}O^{+}$ and $D_{3}O^{+}$ and their hot band rotational lines, and discuss progress in assigning the many unassigned features