The Tibbetts Lab focuses on researching strong-field laser chemistry – chemical reactions induced by strong-field femtosecond laser excitation of gas
Tibbetts group investigates chemical reactions induced by strong-field femtosecond laser excitation of gas- and condensed-phase molecules. The short time duration (~10-14 s) and high electric field strength (~5 V/Å) of femtosecond laser pulses make them ideal for both inducing nonequilibrium chemical transformations and probing reaction dynamics in real time. Current research areas focus on:
- synthesizing metal-based nanoparticles from metal salt precursors and elucidating reaction mechanisms for these transformations in the condensed phase
- probing and controlling the dissociation dynamics of polyatomic radical cations in the gas phase
Synthesis of metal and composite nanoparticles
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 solid surface immersed in the solution enables the synthesis of additional composite nanomaterials with metastable phases. Current projects include controlling metal salt reduction kinetics and metal nanoparticle sizes using hydroxyl radical scavengers, synthesizing ultrasmall metal-oxide and metal-carbon nanocomposite catalysts from metal salt and organometallic precursors, and depositing metal nanoparticles onto silicon laser-induced periodic surface structures (LIPSS) 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.
Dissociation dynamics of gas-phase polyatomic radical cations
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.