Addition Kinetics and Spin Exchange in the Gas Phase Reaction of the Ethyl Radical with Oxygen

Abstract

The kinetics of the addition reaction of O 2 to the ethyl radical has been investigated as a function of temperature (259-425 K) and pressure (1.5-60 bar) using the muon spin relaxation technique in longitudinal magnetic fields. Within this temperature range at 1.5 bar, the chemical reaction is represented by an Arrhenius rate law with an activation energy of -4.4(4) kJ mol -1 and an apparent frequency factor of 1.3(2) × 10 -12 cm 3 molecule -1 s -1 . The high-pressure limit of the rate constant at 294 K amounts to k ch ∞ ) 8.7(8) × 10 -12 cm 3 molecule -1 s -1 . Within error, this limit has been reached at 1.5 bar. The rate coefficient for spin exchange, k ex ) 2.8(2) × 10 -10 cm 3 molecule -1 s -1 , is collision controlled. The results for k ch agree well with experimental literature values, but the temperature dependence is more pronounced than that predicted on the basis of a RRKM extrapolation from low-pressure data. The theoretical basis for the analysis of experimental data is given, and the results are discussed.

From theoretical reaction dynamics to chemical modeling of combustion

“…Ethyl is the smallest alkyl radical for which the R + O 2 potential energy surface exhibits the main features of larger alkyl radicals. Thus, its reaction with O 2 has served as a protopye, with a detailed and quantitative picture of its kinetics derived from extensive experimental [115][116][117][187][188][189][190], electronic structure [191][192][193][194][195][196], and reaction rate theory [117,190,194,[197][198][199][200][201] studies. Building from their early density functional theory analyses [191][192][193], the most important stationary points on the PES were ultimately mapped with a high-level focal point analysis by Schaefer and coworkers [196].…”

“…Plot of the temperature dependence of the recombination rate constant for C 2 H 5 + O 2 . The theoretical results are for the high-pressure limit, while the experimental data are for pressures of ~1 atm of H 2 (Munk et al[114]), He (Kaiser[115]), and N 2 (Dilger et al[116]), or 100 bar of Ar(Fernandes et …”

Muon spin resonance — A variant of magnetic resonance

“…Termination reactions represent also a severe limitation of kinetic work in liquid solution and in the gas phase. Advantage has been taken of the fact that the kinetics is of ideal pseudo-first order if one uses ~tSR [24,25].…”

Experimental and Modeling Study of the Temperature and Pressure Dependence of the Reaction C2H5 + O2 (+ M) → C2H5O2 (+ M)

“…1,2 At room temperature, the experimental pressures varied from very low values, such as realized in very low pressure reactor (VLPR) studies, 10 up to 60 bar as applied in ref 11, with the range 1−1000 Torr being covered most extensively (see, e.g., refs 1, 2, 5, and 12−19). At pressures above about 1 bar, the reaction was found to be close to the high pressure limit of the "normal" falloff curve of the recombination reaction …”

“…No further pressure dependence was observed at pressures up to 60 bar. 11 In the present work, we extended the pressure even more (up to 1000 bar) in order to document the full transition to k 1,∞ . In doing this we were aware of the possibility that the reaction mechanism may change, becoming a superposition of the radical-complex (RC) and the "normal" energy transfer (ET) mechanism.…”