Synchronized Two-Color Time-Resolved Dual-Comb Spectroscopyfor Quantitative Detection of HOx Radicals Formed from Criegee Intermediates

:criegee intermediates, derived from ozonolysis ofalkenes and recognized as key species in the production ofnonphotolytic free radicals, play a crucial role in atmosphericchemistry. Here, we present a spectrometer based on synchronizedtwo-color time-resolved dual-comb spectroscopy, enabling simul-taneous spectral acquisitions in two molecularfingerprint regionsnear 2.9 and 7.8 mu m. Uponflash photolysis of CH2I2/O2/N2gasmixtures, multiple reaction species, involving the simplest Criegeeintermediates (CH2OO), formaldehyde (CH2O), hydroxyl (OH)and hydroperoxy (HO2) radicals are simultaneously detected withmicrosecond time resolution. The concentration of each moleculecan be determined based on high-resolution rovibrationalabsorption spectroscopy. With quantitative detection and simu-lation of temporal concentration profiles of the targeted molecules at various conditions, the underlying reaction mechanisms andpathways related to the formation of the HOxradicals, which can be generated from decomposition of initially energized andvibrationally excited Criegee intermediates, are explored. This approach capable of achieving multispectral measurements withsimultaneously high spectral and temporal resolutions opens up the opportunities for quantification of transient intermediates andproducts, thus, enabling elucidation of complex reaction mechanisms.

Automated summary

In this study, a spectrometer based on synchronized two-color time-resolved dual-comb spectroscopy was developed for simultaneous spectral acquisitions in two molecular fingerprint regions. By using high-resolution rovibrational absorption spectroscopy, the concentration of target molecules can be quantitatively detected and simulated, enabling exploration of reaction mechanisms and pathways related to the formation of HOx radicals.