Hydrogen-atom abstraction from alkanes by hydroxyl. 2. Ethane

Abstract

Absolute rate coefficients for the reactions of OH with C2H6 (kl), C2H3D3 (k2), and C2D6 ( k 3 ) were measured with the laser photolysis/laser-induced fluorescence technique. Kinetic data were obtained at 600 torr of helium pressure over the temperature range 292.5-705 K. The measurements were fit to modified Arrhenius expressions of the form ki(T) = Ail'" exp(-Ei/Rr). Kinetic isotope effects were characterized by two simple relations: k2(T) = 0.5[k1(T) + k 3 ( T ) ] , and k l ( T)/k3(T) = (1.01 A 0.06) exp(907 f 52 cal mol-'/RT), where the quoted uncertainties represent *2u estimates of the total experimental error. Nonempirical electronic structure calculations were performed on the reactants and transition-state structures. They are consistent with and support the experimental findings. (27) Baulch, D. L.; Craven, R. J. B.; Din, M.; Drysdale, D. D.; Grant, S.; Richardson, D. J.; Walker, A.; Watling, G.

Kinetic Study of the Gas-Phase Reaction of OH with Br2

“…For each set of experiments, the difference between the value of k 0 directly measured in the absence of bromine and k 0 found from the zero-abscissa intercept of the least-squares straight line in the ([Br 2 ], k′) coordinates was within the experimental uncertainties (2σ level of statistical uncertainties obtained from the linear least-squares-fits). We analyzed the possible effect of a minor deviation from the first-order kinetic behavior of the OH background loss on the measurement of k 1 values using data processing with the background-loss correction described in references 10, [16][17][18][19]. Under all the experimental conditions in our study, it was found that this effect was very small (less than 0.8% of k 1 value) such that no background-loss correction was necessary.…”

Rate Coefficient and Product Branching Measurements for the Reaction OH + Bromopropane from 230 to 360 K

“…Here, we present the quantification obtained by assuming that (1) the reactivity of a given methyl or methylene group can be suppressed by deuterium substitution without altering the reactivity of the neighboring carbon sites and (2) that the impact of deuteration can be quantified. Tully and co-workers 11,21,22 made the first assumption in their studies of deuterated propanes to determine the reactivity of individual methylene and methyl groups for both hydrogen and deuterium as a function of temperature. The ab initio calculations of Hu et al 23 confirmed, to a first approximation, the reactivity of an individual abstraction site was independent of neighboring alkyl groups.…”

An experimental and theoretical study on the kinetic isotope effect of C2H6 and C2D6 reaction with OH

“…Various approximations have been used in the literature, such as the Next-Nearest-Neighbor (NNN) [5,6] and Structure Activity Relationship (SAR) [7]. Tully and co-workers [8][9][10][11][12][13] pioneered the use of deuterium for the study of deuterium kinetic isotope effect (DKIE) to elucidate rules for the calculation of sitespecific rates of H-abstraction from a variety of hydrocarbon molecules. This methodology has, for example, been used to discern the branching ratios of the two competing channels during the reaction of propane (C 3 H 8 ) with OH at low temperatures [10] and high temperatures [14].…”

“…The aim of the current work is to extend low-temperature (290-800 K) DKIE data of ethane [9] to high temperatures (800 -1350 K) using rate coefficient measurements of the reaction of ethane and deuterated ethane with OH radicals:…”

“…Moreover, a closer look into the database for the rate coefficients of R1 reveals that there are only three direct high-temperature (T > 950 K) measurements available in the literature [16][17][18]. Much of the earlier studies are limited to near room temperatures [9,16,17,[19][20][21][22][23]; and in general they show excellent agreement to each other within overall uncertainties of ± 20% at 298 K [19]. Surprisingly, there are not many reports of theoretical rate constant estimations using the electronic structure methods other than two studies from Krasnoperov and…”