In this project funded by the Chemical Structure, Dynamics and Mechanisms Program of the Division of Chemistry, Professor Lai-Sheng Wang of Brown University, together with his graduate and undergraduate student researchers, will study the structures of large gold clusters and how properties of gold clusters can be modified by dopant atoms. These clusters will be produced by laser vaporization and will be investigated through a combination of mass spectrometry and photoelectron spectroscopy aided by theoretical calculations. The ultimate goal of this research is to understanding the mechanisms of new catalytic properties discovered for gold nanoparticles. Toward this end, the Wang group will also study CO and O2 adsorbed on gold clusters, which will contribute to a molecular-level understanding of CO oxidation by gold nanoparticles.
Another research direction pursued under the support of this program is to study solution phase molecules in the gas phase using electrospray ionization and photoelectron spectroscopy, a unique experimental technique developed in the Wang group. They will focus on the investigation of Au-ligand complexes, aimed at a better understanding of the chemical bonding properties of the gold atom. It has been found in prior research supported under this program that a gold atom can behave like a hydrogen atom in certain Au-containing clusters. The Wang group is interested in probing further the covalent bonding characters of Au with various chemical ligands. Gold complexes have increasingly been found to catalyze important organic transformations in solution. A deeper understanding of the chemical bonding properties of the gold atom can provide insight into the intermediates and mechanisms of homogeneous catalysis by gold complexes.
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.
There are two major goals in this research program: one is to investigate the size-dependent electronic and chemical properties of transition metal clusters and the second goal is to probe the properties of multiply-charged anions and solution-phase metal complexes in the gas phase using photoelectron spectroscopy and high resolution photoelectron imaging. To achieve the first research goal, two state-of-the-art photoelectron spectroscopy apparatuses have been developed and used to probe the electronic, structural, and chemical properties of size-selected gold nanoclusters. Structures of a series of mid-sized gold clusters have been elucidated. The interactions of CO and O2 with size-selected gold clusters have been examined, leading to the observation of important size-dependent chemical reactivities. In particular, the detailed mechanisms of O2 activation by small gold clusters have been studied. Gold nanoparticles have a wide range of applications in catalysis, molecular electronics, and biology. Results and observations obtained from this research program provide basic understanding of the size-dependent electronic and structural properties of gold nanoclusters, which builds the foundation for nanoscience and nanotechnology and may help the development of new applications of gold. A cryogenically-controlled ion trap has been developed to create ultracold anions. This technique has been coupled with the development of a high resolution photoelectron imaging system to allow detailed electronic and vibrational information to be obtained for important solution-phase metal complexes and bio-related molecules. A series of gold-containing complexes have been studied, providing important spectroscopic and electronic structure information to understand the mechanisms of homogenous catalysis by gold complexes. Dipole-bound states have been observed in a number of anions, which have led to the possibility of resonant photoelectron spectroscopy via vibrational autodetachment. This new development not only allows the electronic dynamics in anions to be investigated, but will also lead to a new technique to obtain vibrational spectroscopy of dipolar molecular radical species. Research results obtained from this program has been used in the classroom to strengthen the teaching of nanoscience and physical chemistry by the PI. Students from underrepresented groups have been recruited and trained through this research project. Significant international collaborations have been involved in this program, providing additional training opportunities for the students. The technical development made possible by this project has contributed significantly to research infrastructure of the U.S. and the training of the next generation scientists. Twenty four peer-reviewed publications have been resulted from this project. The PI has delivered twenty two invited talks at academic institutions and national and international conferences on research supported by this grant, in addition to conference presentations by students from this project.
