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Title: Additional chain-branching pathways in the low-temperature oxidation of branched alkanes

Chain-branching reactions represent a general motif in chemistry, encountered in atmospheric chemistry, combustion, polymerization, and photochemistry; the nature and amount of radicals generated by chain-branching are decisive for the reaction progress, its energy signature, and the time towards its completion. In this study, experimental evidence for two new types of chain-branching reactions is presented, based upon detection of highly oxidized multifunctional molecules (HOM) formed during the gas-phase low-temperature oxidation of a branched alkane under conditions relevant to combustion. The oxidation of 2,5-dimethylhexane (DMH) in a jet-stirred reactor (JSR) was studied using synchrotron vacuum ultra-violet photoionization molecular beam mass spectrometry (SVUV-PI-MBMS). Specifically, species with four and five oxygen atoms were probed, having molecular formulas of C 8H 14O 4 (e.g., diketo-hydroperoxide/keto-hydroperoxy cyclic ether) and C 8H 16O 5 (e.g., keto-dihydroperoxide/dihydroperoxy cyclic ether), respectively. The formation of C 8H 16O 5 species involves alternative isomerization of OOQOOH radicals via intramolecular H-atom migration, followed by third O 2 addition, intramolecular isomerization, and OH release; C 8H 14O 4 species are proposed to result from subsequent reactions of C 8H 16O 5 species. The mechanistic pathways involving these species are related to those proposed as a source of low-volatility highly oxygenated species in Earth'smore » troposphere. At the higher temperatures relevant to auto-ignition, they can result in a net increase of hydroxyl radical production, so these are additional radical chain-branching pathways for ignition. Furthermore, the results presented herein extend the conceptual basis of reaction mechanisms used to predict the reaction behavior of ignition, and have implications on atmospheric gas-phase chemistry and the oxidative stability of organic substances.« less
 [1] ;  [2] ;  [3] ;  [4] ;  [1] ;  [5] ;  [6] ;  [3] ;  [4] ;  [6] ;  [3] ;  [7] ;  [1]
  1. King Abdullah Univ. of Science and Technology, Thuwal (Saudi Arabia)
  2. Univ. of Science and Technology of China, Anhui (People's Republic of China)
  3. Sandia National Lab. (SNL-CA), Livermore, CA (United States)
  4. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  5. Physikalisch-Technische Bundesanstalt, Braunschweig (Germany)
  6. Bielefeld Univ., Bielefeld (Germany)
  7. CNRS, INSIS, Orleans Cedex (France)
Publication Date:
Report Number(s):
Journal ID: ISSN 0010-2180; PII: S0010218015004459
Grant/Contract Number:
AC04-94AL85000; DEAC02-05CH11231; AC04-94-AL85000; AC02-05CH11231
Accepted Manuscript
Journal Name:
Combustion and Flame
Additional Journal Information:
Journal Volume: 164; Journal Issue: C; Journal ID: ISSN 0010-2180
Research Org:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE National Nuclear Security Administration (NNSA)
Country of Publication:
United States
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; auto-oxidation; chain-branching; highly oxidized multifunctional molecules; peroxides; alternative isomerization; synchrotron VUV photoionization mass spectrometry
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1249639; OSTI ID: 1379063