An experimental and master-equation modeling study of the kinetics of the reaction between resonance-stabilized (CH3)(2)CCHCH2 radical and molecular oxygen

Show full item record



Permalink

http://hdl.handle.net/10138/334853

Citation

Joshi , S P , Pekkanen , T T , Seal , P , Timonen , R S & Eskola , A J 2021 , ' An experimental and master-equation modeling study of the kinetics of the reaction between resonance-stabilized (CH3)(2)CCHCH2 radical and molecular oxygen ' , Physical Chemistry Chemical Physics , vol. 23 , no. 36 , pp. 20419-20433 . https://doi.org/10.1039/d1cp02210e

Title: An experimental and master-equation modeling study of the kinetics of the reaction between resonance-stabilized (CH3)(2)CCHCH2 radical and molecular oxygen
Author: Joshi, Satya P.; Pekkanen, Timo T.; Seal, Prasenjit; Timonen, Raimo S.; Eskola, Arkke J.
Contributor: University of Helsinki, Department of Chemistry
University of Helsinki, Department of Chemistry
University of Helsinki, Department of Chemistry
University of Helsinki, Department of Chemistry
University of Helsinki, Department of Chemistry
Date: 2021-09-28
Language: eng
Number of pages: 15
Belongs to series: Physical Chemistry Chemical Physics
ISSN: 1463-9076
URI: http://hdl.handle.net/10138/334853
Abstract: The kinetics of the reaction between resonance-stabilized (CH3)(2)CCHCH2 radical (R) and O-2 has been investigated using photoionization mass spectrometry, and master equation (ME) simulations were performed to support the experimental results. The kinetic measurements of the (CH3)(2)CCHCH2 + O-2 reaction (1) were carried out at low helium bath-gas pressures (0.2-5.7 Torr) and over a wide temperature range (238-660 K). Under low temperature (238-298 K) conditions, the pressure-dependent bimolecular association reaction R + O-2 -> ROO determines kinetics, until at an intermediate temperature range (325-373 K) the ROO adduct becomes thermally unstable and increasingly dissociates back to the reactants with increasing temperature. The initial association of O-2 with (CH3)(2)CCHCH2 radical occurs on two distinct sites: terminal 1(t) and non-terminal 1(nt) sites on R, leading to the barrierless formation of ROO(t) and ROO(nt) adducts, respectively. Important for autoignition modelling of olefinic compounds, bimolecular reaction channels appear to open for the R + O-2 reaction at high temperatures (T > 500 K) and pressure-independent bimolecular rate coefficients of reaction (1) with a weak positive temperature dependence, (2.8-4.6) x 10(-15) cm(3) molecule(-1) s(-1), were measured in the temperature range of 500-660 K. At a temperature of 501 K, a product signal of reaction (1) was observed at m/z = 68, probably originating from isoprene. To explore the reaction mechanism of reaction (1), quantum chemical calculations and ME simulations were performed. According to the ME simulations, without any adjustment to energies, the most important and second most important product channels at the high temperatures are isoprene + HO2 (yield > 91%) and (2R/S)-3-methyl-1,2-epoxybut-3-ene + OH (yield < 8%). After modest adjustments to ROO(t) and ROO(nt) well-depths (similar to 0.7 kcal mol(-1) each) and barrier height for the transition state associated with the kinetically most dominant channel, R + O-2 -> isoprene + HO2 (similar to 2.2 kcal mol(-1)), the ME model was able to reproduce the experimental findings. Modified Arrhenius expressions for the kinetically important reaction channels are enclosed to facilitate the use of current results in combustion models.
Subject: BASIS-SET CONVERGENCE
CORRELATED CALCULATIONS
PHOTOIONIZATION
TEMPERATURE
MECHANISM
OXIDATION
ENERGY
HO2
116 Chemical sciences
Rights:


Files in this item

Total number of downloads: Loading...

Files Size Format View
d1cp02210e.pdf 4.587Mb PDF View/Open

This item appears in the following Collection(s)

Show full item record