Femtosecond Studies of the Influence of Solvent on Chemical Reaction Dynamics

University Of Southern California, Los Angeles CA

Investigators

Abstract

In this award, funded by the Chemical Structure, Dynamics and Mechanisms Program of the Chemistry Division, Professor Stephen Bradforth of the University of Southern California and graduate students will study chemical reactions dynamics in water. Novel femtosecond electronic and photoelectron spectroscopies will be employed to unravel ionization, dissociation and proton-coupled electron transfer reaction pathways in water with photochemistry in the phenol family of molecules serving as model systems. The hydrogen atom dissociation and ionization dynamics of phenol and thiophenol, bearing many similarities in reaction dynamics to that of excited-state water but with additional surface-hopping dynamics, will be mapped from gas phase to bulk aqueous phase by new dispersed transient absorption experiments with 30 fs time resolution. These will be complemented by the construction of a new liquid time-resolved photoelectron spectrometer, capable of probing evolution along the reaction coordinate via the photoelectron energy and angular distribution. Initial targets for the liquid-jet spectrometer will be the steady-state angular distributions from inorganic anions of different symmetries and time-resolving phenol excited state chemistry. While this research project focuses specifically on the aqueous phenol system, it will lead to insights into the interplay between solvent motions and solute reactivity that directly impact how most chemists and biochemists design and/or model chemical transformations. The photochemistries of heterocyclic aromatics, including the DNA bases, have related excited state pathways to the phenolic chromophores in solution. Phenol itself is a direct model for tyrosine side chain in proteins where tyrosyl radicals are often significant intermediates in electron transfer activity. A new generation of physical science students will gain vital training in new spectroscopic probes of matter as well as designing and analyzing experiments at the cutting edge of the field. These skills will prepare them for careers in the vital US science and technology sector as well as academic research. Graduate and undergraduate students will have the opportunity to learn from each other and collaborate with international scientists. The Bradforth research group will also participate in outreach efforts at USC to provide hands-on energy-conversion themed summer internships for community-college students serving the largely Hispanic population in South Eastern Los Angeles County. Broad participation of different groups, and collaboration amongst those participants, will continue to be emphasized at all levels of involvement in the project