HO₂ reaction kinetics in an atmospheric pressure plasma jet determined by cavity ring-down spectroscopy

Abstract

HO 2 reaction kinetics in an atmospheric pressure plasma jet determined by cavity ring-down spectroscopyTo cite this article before publication: Michele Gianella et al 2018 Plasma Sources Sci.

A combination of electrochemistry and mass spectrometry to monitor the interaction of reactive species with supported lipid bilayers

“…The remaining · H atoms contribute to the formation of HO 2 · radicals via the reaction with molecular oxygen, yielding to O 2 ·- radicals under the slightly acidic experimental conditions (pH 5–6). An accumulated concentration of ≈ 25 µM was observed, translating into a deposition rate of 1.2 × 10 14 s −1 , fitting published gas phase densities of O 2 ·− /HO 2 · 84 , 85 . Considering the pKa of 4.88 for HO 2 · , 60 to 90% will be dissociated under experimental conditions.…”

Spectroscopy techniques and the measurement of molecular radical densities in atmospheric pressure plasmas

“…Furthermore, we note that the reaction kinetics and pathways of RONS are pH-dependent, adding an additional layer of complexity to the challenges of unravelling the details of the multi-timescale chemistry in these intriguing systems. (a) CRDS spectra of HO2 radicals sampled from a CAP under conditions where the curtain gas is either formed only from O2 or is totally devoid of O2 (dashed lines are fits to the data: see [179]). The total pressure in the sample cell is 40 Torr.…”

“…The same authors have also undertaken both direct and indirect cavity ringdown measurements, examining the influence of curtain gas on the production of HO2 confirming the findings from the previous OF-CEAS experiments and explaining the results in terms of a spatio-dynamic kinetic model. 179 The indirect method employs a sampling procedure in order to transfer the effluent of the CAP into a high finesse cavity working at reduced pressure. While this means a loss of spatio-temporal information and an introduction of uncertainty in the absolute number densities generated by the CAP, it does mean that some of the most sensitive measurements can be made as the twin effects of turbulence and pressure broadening are removed or, at least, minimised.…”

“…Figure 3(b) illustrates how the HO2 concentration varies as a function of the oxygen content of the curtain gas: some HO2 is produced with no curtain gas oxygen, implying that moisture in the carrier gas (argon) is also a potential source of HO2. 179 Another interesting technique suitable for radical detection is Faraday rotation spectroscopy (FRS), which exploits the Faraday effect for the selective detection of paramagnetic species. This involves measuring the rotation of the plane of polarized light upon interaction with a paramagnetic substance in the presence of a longitudinal magnetic field.…”

A Wide-Range and Calibration-Free Spectrometer Which Combines Wavelength Modulation and Direct Absorption Spectroscopy with Cavity Ringdown Spectroscopy

“…The concentration of engine exhaust gases (e.g., NO and CO) in a single internal combustion engine cycle can range from~1 ppm to 0.3% (NO) and~1 ppm to 4% (CO) [15]. There is also quite a large difference in the radial profile of the HO 2 concentrations throughout the plasma effluent in an atmospheric pressure plasma jet [16]. In these cases, such a wide range single method (DAS, CW-CRDS, or CEAS) for fast measurements of gas concentration is difficult to achieve.…”