In this award, funded by the Experimental Physical Chemistry Program of the Division of Chemistry, Professor Lai-Sheng Wang of Washington State University, together with his postdoctoral, graduate and undergraduate student researchers, will study the structural evolution and chemical properties of metal clusters. Topics for investigation include large gold clusters (more than 20 atoms), endohedral gold clusters, tungsten molecules and clusters, as well as gold clusters with chemisorbed CO and oxygen molecules. These species will be studied through a combination of mass spectrometry, photoelectron spectroscopy combined with theoretical methods.
Gold nanoparticles have a wide range of applications in catalysis, molecular electronics and biology. Careful studies like those of Prof. Wang and his group build a knowledge base of the electronic and chemical properties of these species which help to inform the various nanotechnology areas where these substances play a role. The students receiving research training in Prof. Wang's research group will learn to use sophisticated equipment in a unique university/national laboratory environment. Prof. Wang's gold cluster research has captured the public interest, and Prof. Wang continues to be an excellent ambassador for science.
This research program focused on the investigation of the electronic structures of transition-metal clusters and solution-phase molecules in the gas phase. Prof. Wang and his students developed two unique experimental apparatuses for this research, one featured a laser vaporization cluster source to produce atomic clusters and another featured an electrospray ionization source that transported solution-phase anions into the gas phase. Prof. Wang’s group also built a low-temperature electrospray photoelectron spectroscopy apparatus, which can control the temperatures of trapped ions. Atomic clusters, consisting of a few to few hundred atoms, bridge the gap between atoms and bulk matter and form the foundation for nano-science. These clusters, which can be investigated with controlled size and chemical compositions, represent novel chemical systems and extend the concepts of chemical bonding, structures, and reactivity. A major focus of this program was about gold clusters with the objective to help elucidate the remarkable catalytic and electronic properties of gold nanoparticles. Prof. Wang and his students made several advances previously, for example, the discoveries of the highly stable tetrahedral Au20 cluster (the smallest golden pyramid) and the golden buckyballs (Au16– and Au17–). During this funding period, they completed a number of studies on the structures of gold clusters, chemisorption interactions of gold clusters with CO and O2, as well as isomer resolution of gold clusters. They used Ar-tagging and O2 titration to probe the cage to pyramid structural transition between Au16– and Au20–. They found that substitution of a gold atom by a copper or silver atom provided additional information about structural isomers in gold clusters. One of the most significant works concerned the O2 interactions with small gold clusters, Aun– (n = 1–7). Prof. Wang and his students found that the odd-sized clusters (n = 1, 3, 5, 7) formed physisorbed O2-complexes, providing direct spectroscopic evidence that these clusters are nonreactive toward O2. For the even-sized Aun– clusters (n = 2, 4, 6), they obtained vibrationally-resolved spectra, which led to new insights into the O2-Aun cluster interactions. With improved spectroscopic data and computational studies, Prof. Wang and his colleagues were able to obtain definitive structural information for Aun– nano-clusters up to n = 35. Another focus of this program was to study solution-phase molecules and, in particular, multiply-charged anions. Prof. Wang’s group made major progresses in this area and established several international collaborations. Working with scientists from Karlsruhe Institute of Technology, they studied the stability of two multiply-charged anions, the sulfonated pyrene tri- and tetra-anions. Combining photoelectron experimental data with mass spectrometric measurements from Karlsruhe and theoretical calculations by colleagues form Utah State University, they found that the meta-stable trianion had a half-life of 0.1 second. A collaboration with colleagues from Tsinghua University in Beijing was established to study the di-cyanide complexes, M(CN)2– (M = Cu, Ag, Au); experimental and theoretical evidence was obtained on the covalent nature of the Au-C bond in Au(CN)2–. It was further shown that there is significant covalent interaction between Au and I in AuI2– in comparison with that of Cu-I in CuI2–. The covalent interaction of Au is a major topic in chemistry and will be important to understand the role that gold compounds play in many catalytic reactions. The grant allowed partial support of two graduate students and two postdoctoral fellows. One of the students obtained his Ph.D. and is conducting postdoctoral research in another academic institute. The broad collaborations provided a dynamic research environment to train young scientists. Prof. Wang actively uses his research results in his teaching in nanoscience and physical chemistry.
