Addition and elimination reactions on the C4H9• potential-energy surface: Experiments and master-equation analysis of literature data

• Published in: Proceedings of the Combustion Institute 2024, Vol.40 (1-4), Article 105267
• Main Authors: Pekkanen, Timo T., Ramu, Elli A., Timonen, Raimo S., Eskola, Arkke J., Lendvay, György
• Format: Article
• Language: English
• Subjects: Collisional energy transfer; Laser-photolysis photoionization mass spectrometry; Master equation; Reaction kinetics
• ISSN: 1540-7489; 1873-2704
• DOI: 10.1016/j.proci.2024.105267

We have used laser-photolysis photoionization mass spectrometry to determine the unimolecular-decay rate coefficient of the i-butyl radical. Both the pressure (0.5–7 Torr) and temperature dependence (580–690 K) was investigated, and the present work is the first-ever direct kinetic measurement of this reaction. In addition to the experimental work, we have run master-equation simulations to determine addition, elimination, isomerization, and well-skipping rate coefficients for reactions that take place on the ▪ potential-energy surface. A large body of experimental literature data exists for these reactions, which is used together with the current measurements (altogether ∼700 data points) to optimize barrier heights in the master-equation models, as well as to determine collisional-energy-transfer parameters. The optimized master-equation models are able to reproduce experimental findings over a wide range of conditions. We expect the current results to be of use in combustion modeling, and the results output by our master-equation models are given in PLOG format. Due to the abundance of available experimental data, we were able to separately determine collisional-energy-transfer parameters (〈ΔE〉down(300K)) for i-, n-, s-, and t-butyl. These values were obtained for a number of bath gases, including heavy colliders such as CO2 and SF6. It was found that the collisional-energy-transfer parameters are only weakly dependent on the identity of the bath gas. In contrast, the obtained parameters are markedly different for some of the butyl isomers. This is an interesting finding, as it is commonly assumed that isomers have similar collisional-energy-transfer efficiencies. A qualitative explanation based on gateway modes is given to rationalize the finding.