Mid-infrared quantum cascade laser spectroscopy probing of the kinetics of an atmospherically significant radical reaction, $$\hbox {CH}_{3}\hbox {O}_{2}+\hbox {NO}_{2}+\hbox {M}\rightarrow \hbox {CH}_{3}\hbox {O}_{2}\hbox {NO}_{2}+\hbox {M}$$ CH 3 O 2 + NO 2 + M → CH 3 O 2 NO 2 + M , in the gas phase

Abstract

The kinetic parameters of an important atmospheric reaction, $$\hbox {CH}_{3}\hbox {O}_{2} + \hbox {NO}_{2} + \hbox {M}\rightarrow \hbox {CH}_{3}\hbox {O}_{2}\hbox {NO}_{2} + \hbox {M}$$ , have been recorded by monitoring directly the changes in concentrations of methylperoxy radicals $$(\hbox {CH}_{3}\hbox {O}_{2})$$ in the gas phase employing a new mid-infrared quantum cascade laser (QCL)-based apparatus. $$\hbox {CH}_{3}\hbox {O}_{2 }$$ radicals in our apparatus have been generated by pulsed UV laser (266 nm) photolysis of $$\hbox {CH}_{3}\hbox {I}$$ in a gaseous mixture with oxygen. The absorption band corresponding to the mid-infrared O-O stretching fundamental of the peroxy radical, within a narrow spectral range, 1070–1120 $$\hbox {cm}^{-1}$$ , has been recorded by tuning the wavelength of the QCL operated in CW mode. The kinetics of the aforementioned reaction of $$\hbox {CH}_{3}\hbox {O}_{2}$$ with $$\hbox {NO}_{2}$$ has been followed by analyzing the changes of the infrared (QCL) decay profile of $$\hbox {CH}_{3}\hbox {O}_{2}$$ at $$9.1~\upmu \hbox {m}$$ $$(1098.9~\hbox {cm}^{-1})$$ maintaining a pseudo first order reaction condition. We noticed that the rate constant of the reaction at 298 K varies in the range of (1.21–3.08) $$\times 10^{-12}$$ $$\hbox {cm}^{3 }~\hbox {molecule}^{-1 }\,\hbox {s}^{-1 }$$ for changing the total pressure in the range of 75–730 mbar. The absorption cross-section of $$\hbox {CH}_{3}\hbox {O}_{2}$$ at the probe wavelength $$(1098.9~\hbox {cm}^{-1})$$ , has been estimated for the first time to be $$8.3 \pm 0.4 \times 10^{-20}~\hbox {cm}^{2}$$ . Kinetics measurement of an atmospherically important gas phase reaction, $$\hbox {CH}_{3}\hbox {O}_{2}+\hbox {NO}_{2}+\hbox {M}\rightarrow \hbox {CH}_{3}\hbox {O}_{2}\hbox {NO}_{2}+\hbox {M}$$ , is studied using a newly developed apparatus based on pulsed UV laser photolysis time-resolved mid-infrared absorption spectroscopy. $$\hbox {CH}_{3}\hbox {O}_{2}$$ radicals are probed in the mid-infrared by a CW quantum cascade laser (QCL).