RESEARCH
Strong-Field Laser Chemistry to Make and Break Chemical Bonds
Determining unimolecular dissociation mechanisms of radical cations is important to understand fundamental processes including ionizing radiation-induced DNA damage and initial energy release pathways in energetic molecules. Femtosecond time-resolved “pump-probe” measurements can follow these dissociation reactions on their natural timescales. Combined with quantum-chemical calculations of cationic electronic potential energy surfaces and reaction intermediates, these measurements can determine the reaction mechanisms with exquisite detail. Current projects focus on the reactions of organic phosphonates and phosphates as models for the DNA sugar-phosphate backbone and nitrotoluenes as models for nitroaromatic explosives. Future work will explore model systems for the deoxyribose sugar and nucleobases, as well as high-nitrogen content energetic molecules such as tetrazoles.
Metal nanoparticles with tailored sizes possess many unique optical and electronic properties that make them useful for applications such as catalysis and sensing. While many chemical synthetic routes to these types of nanomaterials exist, femtosecond laser reduction of metal salt precursors has the advantages of avoiding the use of environmentally damaging reducing agents and organic surfactants that can limit the practical use of the resulting materials. Combining metal-salt reduction with laser ablation of a target surface (e.g., a Si wafer) immersed in the solution enables the synthesis of metal-oxide composite nanomaterials with metastable phases. Current projects involve determining the effects of added salts and radical scavengers on the reduction kinetics of [AuCl₄]⁻ and size of the resulting Au nanoparticles, synthesizing ultrasmall M@SiOₓ nanocomposites (M=Au, Pd) as CO oxidation catalysts, and synthesizing Au- and Ag-doped laser-induced periodic surface structures (LIPSS) on Si for surface-enhanced Raman spectroscopy (SERS) sensing applications. Future work will focus on extending these synthetic techniques to earth-abundant metals such as Fe, Co, and Ni.
