Research

I. Probing the Electronic Structure of Atomic Clusters Using Size-Selected Anion Photoelectron Spectroscopy

This research is focused on the study of atomic clusters. These clusters, containing 2-200 atoms, are created by focusing an intense laser pulse onto a solid target in a laser vaporization supersonic cluster source. Time-of-flight mass spectrometry is used to analyze the cluster distributions and identify "magic" clusters. The central theme of our research is to understand the chemical structure and chemical bonding of novel clusters through experimental and theoretical studies of their electronic structures. Toward this goal, we have developed a state-of-the-art magnetic-bottle photoelectron spectroscopy apparatus, that allows direct observation of the electronic structures of virtually any clusters. The objectives of this research are: (1) to understand how electrons forming molecular orbitals in small clusters are transformed into energy band in the bulk as cluster size increases; (2) to use clusters as models to understand surface and interface phenomena, (3) to understand the novel physical and chemical properties of the clusters which are intermediate between individual atoms and bulk condensed matter, (4) to discover novel gas-phase molecules and understand their chemical structure and bonding, and (5) bulk syntheses of cluster-based nanomateirals.

Current research projects:
(1) transition metal clusters
(2) environmentally-important oxide clusters
(3) metal-carbon mixed clusters
(4) novel tetracoordinate planar carbon molecules and nonstoichiometric molecules
(5) solid-state synthesis of planar carbon compounds.

II. Investigation of Free Multiply Charged Anions and Their Microscopic Solvation: Probing Solution Chemistry in the Gas Phase

Multiply charged anions are ubiquitous in nature, often found in solutions and solids. Many inorganic, organic, and biomolecules exist as multiply charged anions in solution. However, few multiply charged anions have been studied in the gas phase due to the difficulty of their formation and their intrinsic instability. Multiply charged anions are interesting many-body systems and are important to study from both a fundamental and practical point of view. Electrons in multiply charged anions are bound by a repulsive Coulomb barrier (analogous to that of alpha-particles in heavy nuclei). Investigation of the shape of and tunneling through this potential barrier allows us to understand the stability and lifetime of the anions. Furthermore, investigation of free multiply charged anions and their solvated species can provide microscopic information for understanding solution phase chemistry and inorganic materials involving these anions.

We have developed a new experimental technique to investigate multiply charged anions in the gas phase. An electrospray ion source, in which a solution sample containing the anions is sprayed through a syringe needle under negative bias, is designed and developed to produce multiply charged anions. Ion-trap-time-of-flight mass spectrometry is used to analyze the formed anions. Size- and charge-selected photodetachment photoelectron spectroscopy is used to obtain information about the stability and electronic structure of the anions and their microscopic solvation. We are investigating a wide range of anionic species, which are important in organic, inorganic, and biochemistry, as well as in solid materials and catalysis.

Our laboratory is located in the W. R. Wiley Environmental Molecular Sciences Laboratory (EMSL) at Pacific Northwest National Laboratory in Richland, Washington.