  Dual-comb spectroscopy can provide broad spectral bandwidth and high spectral
resolution in a short acquisition time, enabling time-resolved measurements.
Specifically, spectroscopy in the mid-infrared wavelength range is of
particular interest, since most of the molecules have their strongest
rotational-vibrational transitions in this "fingerprint" region. Here we report
time-resolved mid-infrared dual-comb spectroscopy for the first time, covering
~300 nm bandwidth around 3.3 {\mu}m with 6 GHz spectral resolution and 20
{\mu}s temporal resolution. As a demonstration, we study a CH4/He gas mixture
in an electric discharge, while the discharge is modulated between dark and
glow regimes. We simultaneously monitor the production of C2H6 and the
vibrational excitation of CH4 molecules, observing the dynamics of both
processes. This approach to broadband, high-resolution, and time-resolved
mid-infrared spectroscopy provides a new tool for monitoring the kinetics of
fast chemical reactions, with potential applications in various fields such as
physical chemistry and plasma/combustion analysis.
