Ketone photolysis in the presence of oxygen: A useful source of OH for flash photolysis kinetics experiments

Abstract

Previous studies have shown a significant OH yield from the reaction of RCO radicals (generated from the photolysis of corresponding ketone) with oxygen below total pressures of 200 Torr. The potential of these reactions as a source of OH radicals for flash photolytic kinetic studies is investigated. The viability of the method was tested by measuring rate coefficients for the reaction of OH with ethanol using both acetone/O 2 mixtures and t-butyl hydroperoxide photolysis. The results (with statistical errors at the 2σ level) are in excellent agreement with each other (k EtOH (acetone) = (5.87 ± 0.34) × 10 −18 T 2 exp((515 ± 21)K/T ) cm 3 molecule −1 s −1 and k EtOH (t-butyl hydroperoxide) = (5.27 ± 0.34) × 10 −18 T 2 exp((557 ± 20)K/T ) cm 3 molecule −1 s −1 ) and with the IUPAC recommendation. The reaction of OH with methyl ethyl ketone (2-butanone) has also been investigated using a similar technique. The results show a strong non-Arrhenius temperature dependence, k = (3.84 ± 0.12) × 10 −24 × T 4 × exp((1038 ± 11)/T ). The merits of the ketone/oxygen OH source are contrasted with other established precursors. A major advantage of the technique is the ability to cleanly generate OD without the potential for isotopic scrambling prior to photolysis. C

A combined experimental and theoretical study of reactions between the hydroxyl radical and oxygenated hydrocarbons relevant to astrochemical environments

“…where k 4 is the rate coefficient for reaction (R4). This method, as fully discussed by Carr et al, 26 eliminates the need for additional reagents other than O 2 to be introduced into the chamber. For the experiments of OH with acetone using a nozzle designed for B140 K, and also for all experiments studying the reaction of OH with DME, the 248 nm photolysis of t-BuOOH was used as an OH precursor:…”

“…are the pseudo first order rate coefficients for reactions (R1) and (R4), respectively, t is the reaction time and A is a scaling factor reflecting the non-unity yield of OH from (R4). 26 k diff is the rate of diffusion of OH radical out of the laser overlap region in the supersonic flow. 25 Eqn (E4) was fitted to the experimental data for the time profile of OH to give k 1 0 + k diff and the bimolecular rate coefficient k 1 0 was determined as the gradient of a plot of…”

Analysis of the Kinetics and Yields of OH Radical Production from the CH3OCH2 + O2 Reaction in the Temperature Range 195–650 K: An Experimental and Computational study

“…24,31,[36][37][38][39] The CH3OCH2 or OH radical precursor(s), reactant (O2), and buffer gas (He or N2) were premixed in a mixing manifold before being flowed through the reaction cell.…”

“…However, Carr et al 37 have shown that photolysis of acetone at 248 nm in the presence of O2 is a potential source of OH:…”

Multiplicative algorithm for discriminating between Arrhenius and non-Arrhenius behaviour

“…In our examples, the initial best guesses come from real experimental works [30][31][32][33] and the optimum designs obtained are robust against deviations of the initial estimates of parameters. It seems convenient to perform a thorough analysis of the behaviour of the T-optimal designs when the hypothesis or conditions assumed for their construction differ from the actual ones.…”