Direct Frequency Comb Measurement of OD + CO -> DOCO Kinetics

TL;DR

This study uses advanced frequency comb spectroscopy to directly observe and quantify the formation of the HOCO intermediate in the OD + CO reaction, confirming its mechanism and dependence on pressure and bath gases.

Contribution

First direct observation of trans-DOCO in the OD + CO reaction at thermal conditions using frequency comb spectroscopy, providing new insights into HOCO formation mechanisms.

Findings

Confirmed low-pressure termolecular dependence of reaction rate

Quantified HOCO yield in OD + CO reaction

Validated HOCO formation mechanism

Abstract

The kinetics of the OH + CO reaction, fundamental to both atmospheric and combustion chemistry, are complex due to the formation of the HOCO intermediate. Despite extensive studies on this reaction, HOCO has not been observed at thermal reaction conditions. Exploiting the sensitive, broadband, and high-resolution capabilities of time-resolved cavity-enhanced direct frequency comb spectroscopy, we observe OD + CO reaction kinetics with the detection of stabilized trans-DOCO, the deuterated analogue of trans-HOCO, and its yield. By simultaneously measuring the time-dependent concentrations of both trans-DOCO and OD species, we observe unambiguous low-pressure termolecular dependence on the reaction rate coefficients for both N2 and CO bath gases. These results confirm the HOCO formation mechanism and quantify its yield.