An instrument to measure fast gas phase radical kinetics at high temperatures and pressures

Stone, Daniel; Blitz, Mark A.; Ingham, T.; Onel, Lavinia; Medeiros, Diogo J.; Seakins, Paul W.

doi:10.1063/1.4950906

Cited by 11 publications

(17 citation statements)

References 61 publications

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“…15 A major issue when sampling the monitored species prior to detection, is whether the transit time from the sampling pinhole to detection influences the kinetic measurements. 18,[77][78][79] In this study, room temperature pseudo-first-order rate coefficients of up to 70,000 s -1 are in excellent agreement with the literature data. At higher first order rate coefficients, the influence of transport can be observed, but can potentially be accounted for with a biexponential analysis.…”

Section: S1supporting

confidence: 90%

“…27 Additionally, proton-transfer reaction time of flight mass spectrometry (Kore Technology, Series I PTR-TOF-MS), was employed for a qualitative verification of the product of the allylic hydrogen abstraction by OH radicals. The exhaust gas from the high pressure high temperature apparatus, described previously 18 was vented to atmospheric pressure and subsequently sampled into the PTR-MS spectrometer.…”

Section: Methodsmentioning

confidence: 99%

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Kinetics of the Reaction of OH with Isoprene over a Wide Range of Temperature and Pressure Including Direct Observation of Equilibrium with the OH Adducts

et al. 2018

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The reaction of the OH radical with isoprene, CH (R1), has been studied over the temperature range 298-794 K and bath gas pressures of nitrogen from 50 to 1670 Torr using laser flash photolysis (LFP) to generate OH and laser-induced fluorescence (LIF) to observe OH removal. Measurements have been made using both a conventional LFP/LIF apparatus and a new high pressure system. The measured rate coefficient at 298 K ( k = (9.90 ± 0.09) × 10 cm molecule s) in the high pressure apparatus is in excellent agreement with the literature, confirming the accuracy of measurements made with this instrument. Above 700 K, the OH decays were no longer single exponentials due to regeneration of OH from adduct decomposition and the establishment of the OH + CH ⇌ HOCH equilibrium (R1a, R-1a). This equilibrium was analyzed by comparison to a master equation model of reaction R1 and determined the well depth for OH addition to carbon C and C to be equal to 153.5 ± 6.2 and 143.4 ± 6.2 kJ mol, respectively. These well depths are in excellent agreement with the present ab initio-CCSD(T)/CBS//M062X/6-311++G(3df,2p)-calculations (154.1 kJ mol for the C adduct). Addition to the less stable C and C adducts is not important. The data above 700 K also indicated that a minor but significant direct abstraction channel, R1b, was also operating with k = (1.3 ± 0.3) × 10 exp(-3.61 kJ mol/ RT) cm molecule s. Additional support for the presence of this abstraction channel comes from our ab initio calculations and from room-temperature proton transfer mass spectrometry product analysis. The literature data on reaction R1 together with the present data were assessed using master equation analysis, using the MESMER package. This analysis produced a refined data set that generates our recommended k( T, [ M]). An analytical representation of k( T, [ M]) and k( T, [ M]) is provided via a Troe expression. The reported experimental data (the sum of addition and abstraction), k = (9.5 ± 0.2) × 10( T/298 K) + (1.3 ± 0.3) × 10 exp(-3.61 kJ mol/ RT) cm molecule s, significantly extend the measured temperature range of R1.

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Section: S1supporting

confidence: 90%

Section: Methodsmentioning

confidence: 99%

Kinetics of the Reaction of OH with Isoprene over a Wide Range of Temperature and Pressure Including Direct Observation of Equilibrium with the OH Adducts

et al. 2018

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“…true kinetics of the OH decay can lead to underestimations of very high reactivities; this is described in detail by Stone et al (2016). Successful measurements with known concentrations of CH 4 at reactivities of ∼ 150 s −1 (Sect.…”

Section: Effects Of Averaging Time and Future Improvements To Samplingmentioning

confidence: 99%

Measurement of OH reactivity by laser flash photolysis coupled with laser-induced fluorescence spectroscopy

et al. 2016

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Abstract. OH reactivity (k OH ) is the total pseudo-first-order loss rate coefficient describing the removal of OH radicals to all sinks in the atmosphere, and is the inverse of the chemical lifetime of OH. Measurements of ambient OH reactivity can be used to discover the extent to which measured OH sinks contribute to the total OH loss rate. Thus, OH reactivity measurements enable determination of the comprehensiveness of measurements used in models to predict air quality and ozone production, and, in conjunction with measurements of OH radical concentrations, to assess our understanding of OH production rates. In this work, we describe the design and characterisation of an instrument to measure OH reactivity using laser flash photolysis coupled to laserinduced fluorescence (LFP-LIF) spectroscopy. The LFP-LIF technique produces OH radicals in isolation, and thus minimises potential interferences in OH reactivity measurements owing to the reaction of HO 2 with NO which can occur if HO 2 is co-produced with OH in the instrument. Capabilities of the instrument for ambient OH reactivity measurements are illustrated by data collected during field campaigns in London, UK, and York, UK. The instrumental limit of detection for k OH was determined to be 1.0 s −1 for the campaign in London and 0.4 s −1 for the campaign in York. The precision, determined by laboratory experiment, is typically < 1 s −1 for most ambient measurements of OH reactivity. Total uncertainty in ambient measurements of OH reactivity is ∼ 6 %. We also present the coupling and characterisation of the LFP-LIF instrument to an atmospheric chamber for measurements of OH reactivity during simulated experiments, and provide suggestions for future improvements to OH reactivity LFP-LIF instruments.

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“…The current paper describes a significant development on our earlier FAGE-based instrument for time-resolved OH detection (Stone et al, 2016). In this improved system, laser flash photolysis in a high-pressure (up to 5 bar), temperaturecontrollable (300-800 K) reactor (shown in Fig.…”

Section: Introductionmentioning

confidence: 99%

A new instrument for time-resolved measurement of HO<sub>2</sub> radicals

et al. 2020

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Abstract. OH and HO2 radicals are closely coupled in the atmospheric oxidation and combustion of volatile organic compounds (VOCs). Simultaneous measurement of HO2 yields and OH kinetics can provide the ability to assign site-specific rate coefficients that are important for understanding the oxidation mechanisms of VOCs. By coupling a fluorescence assay by gaseous expansion (FAGE) laser-induced fluorescence (LIF) detection system for OH and HO2 with a high-pressure laser flash photolysis system, it is possible to accurately measure OH pseudo-1st-order loss processes up to ∼100 000 s−1 and to determine HO2 yields via time-resolved measurements. This time resolution allows discrimination between primary HO2 from the target reaction and secondary production from side reactions. The apparatus was characterized by measuring yields from the reactions of OH with H2O2 (1:1 link between OH and HO2), with C2H4∕O2 (where secondary chemistry can generate HO2), with C2H6∕O2 (where there should be zero HO2 yield), and with CH3OH∕O2 (where there is a well-defined HO2 yield). As an application of the new instrument, the reaction of OH with n-butanol has been studied at 293 and 616 K. The bimolecular rate coefficient at 293 K, (9.24±0.21)×10-12 cm3 molec.−1 s−1, is in good agreement with recent literature, verifying that this instrument can measure accurate OH kinetics. At 616 K the regeneration of OH in the absence of O2, from the decomposition of the β-hydroxy radical, was observed, which allowed the determination of the fraction of OH reacting at the β site (0.23±0.04). Direct observation of the HO2 product in the presence of oxygen has allowed the assignment of the α-branching fractions (0.57±0.06) at 293 K and (0.54±0.04) at 616 K, again in good agreement with recent literature; branching ratios are key to modelling the ignition delay times of this potential “drop-in” biofuel.

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An instrument to measure fast gas phase radical kinetics at high temperatures and pressures

Cited by 11 publications

References 61 publications

Kinetics of the Reaction of OH with Isoprene over a Wide Range of Temperature and Pressure Including Direct Observation of Equilibrium with the OH Adducts

Kinetics of the Reaction of OH with Isoprene over a Wide Range of Temperature and Pressure Including Direct Observation of Equilibrium with the OH Adducts

Measurement of OH reactivity by laser flash photolysis coupled with laser-induced fluorescence spectroscopy

A new instrument for time-resolved measurement of HO<sub>2</sub> radicals

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An instrument to measure fast gas phase radical kinetics at high temperatures and pressures

Cited by 11 publications

References 61 publications

Kinetics of the Reaction of OH with Isoprene over a Wide Range of Temperature and Pressure Including Direct Observation of Equilibrium with the OH Adducts

Kinetics of the Reaction of OH with Isoprene over a Wide Range of Temperature and Pressure Including Direct Observation of Equilibrium with the OH Adducts

Measurement of OH reactivity by laser flash photolysis coupled with laser-induced fluorescence spectroscopy

A new instrument for time-resolved measurement of HO&lt;sub&gt;2&lt;/sub&gt; radicals

Contact Info

Product

Resources

About

A new instrument for time-resolved measurement of HO<sub>2</sub> radicals