Richard Saykally of the University of California, Berkeley is supported by an award from the Chemical Structures, Dynamics and Mechanisms program in the Chemistry Division to further develop and extend his high precision Terahertz vibration-rotation-tunneling (VRT) spectroscopy measurements of small water clusters. Results from these measurements are being used to calibrate and test new theoretical approaches in order to achieve the goal of a "universal first-principles" model of water. Professor Saykally and his research group focus on the complete characterization of the isotopomers of dimer-hexamer water clusters to develop and validate theoretical descriptions of the complicated man-body interactions that are important for water in the condensed phases. They are also extending these approaches to treat larger later clusters, protonated water clusters, and clusters of water with nitrogen oxygen and hydrocarbons.
Because water is such a ubiquitous substance on our planet as well as crucial for the existence of life, it is important to understand its intrinsic nature as well as its interaction with other substances. An accurate model of water is crucial for proper calculation of many biological structures and functions, as well as for understanding critical environmental issue such as global warming. While great advances have been made in developing these models, they are still not accurate enough for many important applications. The PI actively reaches out to increase the public understanding of the nature of water through public lectures, the media and other venues. Undergraduates, graduate students and postdoctoral researchers, including many women, take part in this research program.
In 2007, the PI was among a group of scientists who were asked by noted science writer Michael Schirber to identify for an article appearing on LiveScience(www.livescience.com) what they viewed as "the most important unsolved mystery in science", to which he responded "The greatest mystery in science is understanding why, after literally centuries of tireless research and endless debate, we remain unable to accurately describe and predict the properties of water-the ostensibly simple third most abundant molecule in The Universe, and the basis of all life as we know it" . The research funded by this NSF grant was designed to advance our understanding of water. Specifically, we seek to develop a "universal predictive model" for water in all its forms, such that any question about water, or subsequently , water solutions, could be answered by a suitable computer calculation. We seek to accomplish this by combining highly detailed measurements of water clusters made by terahertz laser spectroscopy(a technology that our group pioneered two decades ago) with the best available computer calculations. We have published many papers on this subject, addressing the water dimer, trimer, tetramer, pentamer, and hexamer. In the current grant period, we focused primarily on the development and employment of new technologies for terahertz spectroscopy, necessary to replace our aged and obsolete laser spectrometer. We collaborated with Prof. Peter Siegel from Cal Tech ito explore the use of their state of the art high frequency multipliers in our experiments, successfully detecting terahertz spectra of the water trimer and pentamer, but not the water octamer-a prime target of the study that had been detected years before. Higher power sources are needed for this endeavor. We also collaborated with Dr. Alan Lee of Longwave Inc on the testing of highly novel quantum cascade lasers for the same purpose. These are much higher power source of terahertz light, but they are much higher to operate, and they are complimentary to the multiplier sources in that the work better at higher frequencies. while we were able to detect spectra of the water dimer, there were serious artifacts in spectra taken with the QCLs that precluded further study. Mitigation of these issues has been under consideration at Longwave, as we prepare for a second test run. During the testing of the Cal Tech source, we were able to accurately measure a large number of new spectra of the water-methane dimer(Fig 1). We are actively working with several theory groups to assign and analyze these spectra, and to subsequently initiate the determination of a computer model for the interaction of water and methane that can be used for more accurate predictions of the properties of methane clathrates-which comprise the largest known reservoir of hydrocarbons on the Earth We have published one paper on the water octamer, featuring our older data, and several other papers related to previously funded studies, and the PI has given a number of invited lectures on the NSF-funded work. Two graduate students were supported by this grant, with one(Orion Shih) completing her PhD. Two undergraduates and two postdocs also worked on this project, as did Prof. Wei Lin from The University of Texas-Brownsville, supported by a DOE grant for faculty from universities serving underrepresented minorties. Figure 1. Measured terahertz spectra of the water-methane dimer, compared with theoretical predictions made by Prof C. Leforestier of Montpelier, France.
