Reflected Shock Tube Studies of High-Temperature Rate Constants for OH + CH₄→ CH₃+ H₂O and CH₃+ NO₂→ CH₃O + NO

Abstract

The reflected shock tube technique with multipass absorption spectrometric detection of OH radicals at 308 nm has been used to study the reactions OH + CH(4) --> CH(3) + H(2)O and CH(3) + NO(2) --> CH(3)O + NO. Over the temperature range 840-2025 K, the rate constants for the first reaction can be represented by the Arrhenius expression k = (9.52 +/- 1.62) x 10(-11) exp[(-4134 +/- 222 K)/T] cm(3) molecule(-1) s(-1). Since this reaction is important in both combustion and atmospheric chemistry, there have been many prior investigations with a variety of techniques. The present results extend the temperature range by 500 K and have been combined with the most accurate earlier studies to derive an evaluation over the extended temperature range 195-2025 K. A three-parameter expression describes the rate behavior over this temperature range, k = (1.66 x 10(-18))T(2.182) exp[(-1231 K)/T] cm(3) molecule(-1) s(-1). Previous theoretical studies are discussed, and the present evaluation is compared to earlier theoretical estimates. Since CH(3) radicals are a product of the reaction and could cause secondary perturbations in rate constant determinations, the second reaction was studied by OH radical production from the fast reactions CH(3)O --> CH(2)O + H and H + NO(2) --> OH + NO. The measured rate constant is 2.26 x 10(-11) cm(3) molecule(-1) s(-1) and is not dependent on temperature from 233 to 1700 K within experimental error.

Shock tube measurements of high temperature rate constants for OH with cycloalkanes and methylcycloalkanes

“…For OH detection at 308 nm, a White cell, radially located at 6 cm from the endplate (as described previously [16][17][18]) was used to increase the absorption path length. It was constructed from two flat fused silica windows (3.81 cm), mounted on the tube across from one another, with broadband antireflection (BB AR) coating for UV light.…”

“…These reflectors were attached to adjustable mounts, and the center points of windows and mirrors were all in a coaxial position. With this new configuration, 48 multiple passes were used, thereby amplifying the measured absorbances by about a factor of ∼4.5 over that used in the previous work [17,18]. This increase in sensitivity for OH-radical detection allows for the detection of lower [OH] and therefore decreases the importance of secondary reaction perturbations.…”

“…(24) derived from the sum of Eqs. (18) and (19). There is only one tertiary abstraction site yielding MCP(rad4) + H 2 O, and its rate constant is given by Eq.…”

Influence of EGR compounds on the oxidation of an HCCI-diesel surrogate

“…Conversion of benzyl with NO 2 generating alkoxybenzyl radicals with the same reaction-rate constants as defined for the reaction between methyl radicals and NO 2 [32].…”

Sensitizing effects of NOx on CH4 oxidation at high pressure

“…Glarborg et al [67] re-analyzed the experimental data from Glänzer and Troe [56], Hsu and Lin [64], and Zhang and Bauer [66], recommending the high-and low-pressure limiting rate coefficients proposed by Glänzer and Troe, together with a center-broadening factor of F cent,32 = 0.183. Data on the disproportionation reaction (R10) [56][57][58][59][67][68][69] indicate a rate constant that is largely independent of temperature.…”