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

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

Abstract

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.

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