Long-wave mid-infrared time-resolved dual-comb spectroscopy of short-lived intermediates

In this Letter, an electro-optic dual-comb spectrometer with a central tunable range of 7.77-8.22 µm is demonstrated to perform transient absorption spectroscopy of the simplest Criegee intermediate (CH₂OO), a short-lived species involved in many key atmospheric reactions, and its self-reaction product via comb-mode-resolved spectral sampling at microsecond temporal resolution. By combining with a Herriott-type flash photolysis cell, CH₂OO can be probed with a detection limit down to ∼1×10¹¹moleculescm^-3. Moreover, pressure broadening of CH₂OO absorption lines can be studied with spectrally interleaved dual-comb spectroscopy. This Letter holds promise for high-resolution precision measurements of transient molecules, especially for the study of large molecules in complex systems.