Terahertz Spectroscopy of Ions and Clusters at the Saykally Group

http://www.cchem.berkeley.edu/rjsgrp/joomla/index.php?option=com_content&view=category&layout=blog&id=11&Itemid=9

Orion Shih, Frank Liu

Technical Developments

Currently, two CW Terahertz laser experiments and one diode laser experiment are in operation. Technological goals include extension of the operating range to frequencies above 5 terahertz, theincorporation of tunable quantum cascade lasers in the Far-IR/Terahertz region, and the extension of the VRT spectroscopy approach to ionic clusters and free radical clusters.

We have measured extensive and highly detailed spectra of the water dimer, trimer, tetramer, pentamer, and hexamer, which characterize the hydrogen bonding interactions and the hydrogen tunneling dynamics in these clusters. Using new theoretical developments, these data arebeing used to develop a universal "first principles" water force field to describe water in all of its forms under wide ranges of conditions. Current efforts involve extension to PROTONATED waterclusters and hydrated free radicals of atmospheric interest.


Building Liquids-One Step at a Time

By the rigorous and systematic investigation of clusters by a combination of theory and VRT spectroscopy, we can untangle the complexities resulting from the many-body interactions that are soprominent in strongly associating liquids, like water. For water, we have carried out detailed studies of dimer, trimer, tetramer, pentamer, and hexamer. While the characterization of these smallclusters still needs to be completed, we seek to extend this work to larger clusters. One product of this work is the construction of a "Universal Force Field" that can be used to describe water in all ofits forms under a wide range of conditions. See publication 316.





The Hydrated Proton

The nature of the proton transfer process influences many chemical and biological processes, but remains quite incompletely understood. We are approaching this by the sequential study of protonated water clusters with Terahertz/FIR VRT spectroscopy and theory, followingthe same approach used for neutral water clusters and using recent results from mid-IR spectroscopy to guide the experiments. See publication 310.

Free Radical Hydrate Complexes

It is now recognized that water complexes of radical species like ClO and HO could comprise an important and presently uncharacterized reservoir of reactive molecules in the atmosphere. We seek to investigate these complexes by a rigorous combination of theory and VRT spectroscopy.