Laser Spectroscopy of Ions and Clusters

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Richard J. Saykally of the University of California in Berkeley is supported by the Experimental Physical Chemistry Program in his continuing studies of clusters using infrared spectroscopy. The goal is to determine structure, force fields and hydrogen bond network rearrangements in water clusters (hexamer, octamer and larger) using far infrared (FIR) laser vibration-rotation-tunneling (VRT) spectroscopy or infrared-cavity ring down laser absorption spectroscopy (IR-CRLAS). A water-water pair potential will be derived from analysis of the dimer spectra, and an effective potential for the larger clusters and liquid water will be constructed. Prof. Saykally will also investigate intermolecular dynamics of nucleotide bases and their hydrated clusters. To support these studies, a number of technological advances are planned including extension of the CRLAS deeper into the mid-IR and development of a new FIR laser with a ring cavity design. Establishing a detailed and quantitative understanding of liquid water continues to be a problem of major importance. While the intriguing properties of supercooled water and hydrophobic interactions occupy the interest of many prominent chemists and physicists, the more mundane problem of accurately describing the ordinary liquid over a wide range of temperatures is of considerable practical importance. This project will enhance our understanding of the liquid and solid phases of water by examining successively larger clusters one molecule at a time, and studying these clusters in great detail with new laser technology and state-of-the-art theoretical methods. The resulting data will ultimately provide a more detailed description of the important many body forces operating in the liquid. The newer effort involving studies of hydrogen bonding of water with nucleotide bases is clearly of fundamental significance in biology.