State-Resolved Spectroscopy and Dynamics of Chemical Transients

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Through this award, funded by the Chemical Structure, Dynamics, and Mechanisms Program of the Division of Chemistry, Prof. David J. Nesbitt from JILA/University of Colorado will use state-of-the-art chemical physics methods to investigate fundamental problems involving highly reactive molecular transients, ranging from atmospheric chemistry at the marine boundary to chemistry in the interstellar medium. The overall goals of this experimental program are threefold: i) exploit high sensitivity direct absorption IR laser methods for study of fundamental jet cooled molecular ions, clusters and molecular ion clusters in slit supersonic discharge expansions, ii) develop and implement novel spectroscopic tools for quantum state-resolved collision studies at gas-ionic solution and gas-liquid microjet interfaces, and iii) utilize the powerful combination of time resolved fluorescence microscopy and laser "nanobathtub" heating methods for fundamental chemical physics studies of temperature and viscosity dependent RNA folding/unfolding at the single molecule level.The way molecules interact to form a liquid or a solid is generally driven by relatively weak forces, which can be studied in detail by laser spectroscopy of small clusters of these species. In a similar vein, these spectroscopic tools can also be extended to probe the interactions of molecules colliding at the gas-liquid interface, specifically investigating with what probability they dissolve in the top liquid layer and how often they simply "bounce" back into the gas phase. In a very real sense, these studies permit one to interrogate the chemical composition of the molecules at the gas-liquid interface. Finally, we have built instruments that can focus laser pulses in a microscope lens down to a small enough spot size to illuminate a single fluorescent label (i.e., the Donor) in a doubly labeled RNA biomolecule with a second fluorescent label (i.e., the Acceptor). By monitoring the color, time, and polarization of the light that gets reemitted, we can learn about the proximity of the two dye labels, which allows us to watch in real time (i.e., msec to sec to minutes), for example, the kinetics for forming double stranded DNA from single strands, or the folding of a single protein into a competent, enzymatically active structure. This work will enable the training of graduate and undergraduate students in advanced areas of chemical physics (e.g., quantum optics, lasers, plasmas, and electronics), while furthering the discovery of fundamental new research knowledge. The results of these studies will provide opportunities for student participation in national professional meetings, outreach through scientific open houses, mentoring with the local high schools, as well as operation of the "CU Wizards" Science Outreach Program for elementary and middle school students.