Direct frequency comb measurement of OD + CO → DOCO kinetics

Area of Science:

• Atmospheric Chemistry
• Combustion Chemistry
• Chemical Kinetics

Background:

• The hydroxyl radical (OH) + carbon monoxide (CO) reaction is crucial for atmospheric and combustion processes.
• The formation of the hydrocarboxyl radical (HOCO) intermediate complicates the reaction kinetics.
• HOCO has not been previously observed under thermal reaction conditions.

Purpose of the Study:

• To investigate the kinetics of the deuteroxyl radical (OD) + CO reaction.
• To detect and characterize the trans-DOCO intermediate, the deuterated analog of HOCO.
• To confirm the HOCO formation mechanism and quantify its yield.

Main Methods:

• Utilized time-resolved cavity-enhanced direct frequency comb spectroscopy.
• Measured time-dependent concentrations of trans-DOCO and OD species.
• Analyzed low-pressure termolecular dependence of reaction rate coefficients.

Main Results:

• Successfully detected stabilized trans-DOCO.
• Observed unambiguous low-pressure termolecular dependence for N2 and CO bath gases.
• Provided kinetic data confirming the HOCO formation mechanism.

Conclusions:

• The study confirms the HOCO formation mechanism in the OH + CO reaction.
• Quantified the yield of the HOCO intermediate.
• Demonstrated the utility of advanced spectroscopic techniques for studying complex reaction kinetics.