About the Lab
A major focus of our research program is the synthesis and characterization of novel atomic and molecular clusters containing metals. These clusters may consist of only a few atoms of pure metal, mixtures of metals, or metal compounds (carbides, oxides, etc.), or they may be a metal center with one or more molecules attached to it. The overall goal is the elucidation of the chemical bonding between metals and at the metal-molecular interface. The work is fundamental, but practical implications are easily found in heterogeneous catalysis, physisorption on metal surfaces, production of microelectronic materials, metal-ligand bonding, metal ion solvation, atmospheric meteor ablation chemistry, astrophysics and interstellar dust, and interactions in metal and semiconductor plasmas. In all projects, the metal systems are produced in a gas phase/molecular beam environment using pulsed laser vaporization of metal targets. The resulting clusters and/or metal complexes are analyzed and size selected using time-of-flight mass spectrometers. A significant component of the research focuses on the design and optimization of time-of-flight mass spectrometers. High resolution spectroscopy measurements are conducted using a variety of tunable visible, ultraviolet, and infrared lasers, using the techniques of laser induced fluorescence, multiphoton ionization and photodissociation spectroscopy. These studies investigate the electronic orbital energies, bonding configurations, ionization potentials, vibrational frequencies, bond energies, bond distances, geometric structures and photochemical pathways in the clusters. We study neutral clusters as well as positive and negative ions.
Another major effort includes the study of proton accommodation and proton transfer dynamics in molecular networks. Proton transfer is a critical aspect of biological energy transfer and hydrogen fuel cell operation, and protonated molecules are active components of atmospheric and interstellar ion chemistry. We produce gas phase ions and clusters containing protons bound to inorganic, organic and organometallic systems and use size-selected infrared spectroscopy to probe the structures resulting from proton binding. Systems of recent interest include protonated water clusters, proton-shared molecular dimers of nitrogen, CO, CO2, acetone, etc., and protonated organic molecules including protonated acetylene, ethylene, benzene, naphthalene, etc.
Students interested in graduate or postdoctoral work in the Duncan lab can contact Dr. Duncan directly at the addresses given above. Dr. Duncan is an Alexander von Humboldt Fellow and therefore postdoctoral applicants who are German or Swiss citizens can also apply to the Humboldt Foundation for financial support to work in the Duncan labs.
- Metal Ion Complexes
- Protonated Water Clusters
- Other Protonated Molecular Clusters
- Metal-Carbide and Oxide Cages and Nanocrystals
- Novel Organometallic Clusters
- Laser Desorption Mass Spectrometry of Thin Films
- Synthesis of Ligand-Coated Nanoparticle Materials
This is a photograph of the inside of one of our "source" chambers where clusters are produced. The sample in this example is a silver rod hanging down from above that is mounted in a special holder. The laser comes through the window on the opposite side and hits this rod as it is rotating. A spray of helium or argon gas flows over the metal rod surface where the laser hits it. The metal-containing cluster molecules spray out of this (toward the right in this figure) and the center part of this spray goes through the hole in the "skimmer" (the silver cone-shaped device mounted on the right wall). This gas then goes into an adjacent vacuum chamber where the mass spectrometer is located.
Here is a photograph of one of our beam machines with the reflectron time-of-flight mass spectrometer (our lab has three of these instruments):
Clusters are produced in the source chamber on the right (see expanded photo above) and then they flow through the skimmer into the second chamber at left where the mass spectrometer is loctated. Two pipes come out of this chamber to make the flight tube for the time-of-flight mass spectrometer. The ions are reflected down the second pipe in the turning region, which is the can closest and to the left. This is where the laser excites the ions.