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J Phys Chem Lett. 2014 Jul 3;5(13):2241-6. doi: 10.1021/jz5008559. Epub 2014 Jun 16.

Mid-Infrared Time-Resolved Frequency Comb Spectroscopy of Transient Free Radicals.

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†JILA, National Institute of Standards and Technology and University of Colorado, Department of Physics, 440 UCB, Boulder, Colorado 80309, United States.
‡Material Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899, United States.
§Arthur Amos Noyes Laboratory of Chemical Physics, Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States.


We demonstrate time-resolved frequency comb spectroscopy (TRFCS), a new broadband absorption spectroscopy technique for the study of trace free radicals on the microsecond timescale. We apply TRFCS to study the time-resolved, mid-infrared absorption of the deuterated hydroxyformyl radical trans-DOCO, an important short-lived intermediate along the OD + CO reaction path. Directly after photolysis of the chemical precursor acrylic acid-d1, we measure absolute trans-DOCO product concentrations with a sensitivity of 5 × 10(10) cm(-3) and observe its subsequent loss with a time resolution of 25 μs. The multiplexed nature of TRFCS allows us to detect simultaneously the time-dependent concentration of several other photoproducts and thus unravel primary and secondary chemical reaction pathways.


HOCO radicals; chemical kinetics; frequency combs; mid-infrared spectroscopy; time-resolved spectroscopy


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