Molecular weight growth in Titan's atmosphere: Branching pathways for the reaction of 1-propynyl radical (H3CC≡C˙) with small alkenes and alkynes

Kirk, Benjamin B.; Savee, John D.; Trevitt, Adam J.; Osborn, David L.; Wilson, Kevin R.

doi:10.1039/c5cp02589c

Title: Molecular weight growth in Titan's atmosphere: Branching pathways for the reaction of 1-propynyl radical (H₃CC≡C˙) with small alkenes and alkynes

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Abstract

The reaction of small hydrocarbon radicals (i.e. ˙CN, ˙C₂H) with trace alkenes and alkynes is believed to play an important role in molecular weight growth and ultimately the formation of Titan's characteristic haze. Current photochemical models of Titan's atmosphere largely assume hydrogen atom abstraction or unimolecular hydrogen elimination reactions dominate the mechanism, in contrast to recent experiments that reveal significant alkyl radical loss pathways during reaction of ethynyl radical (˙C₂H) with alkenes and alkynes. In this study, the trend is explored for the case of a larger ethynyl radical analogue, the 1-propynyl radical (H3CC≡C˙), a likely product from the high-energy photolysis of propyne in Titan's atmosphere. Using synchrotron vacuum ultraviolet photoionization mass spectrometry, product branching ratios are measured for the reactions of 1-propynyl radical with a suite of small alkenes (ethylene and propene) and alkynes (acetylene and d₄-propyne) at 4 Torr and 300 K. Reactions of 1-propynyl radical with acetylene and ethylene form single products, identified as penta-1,3-diyne and pent-1-en-3-yne, respectively. These products form by hydrogen atom loss from the radical-adduct intermediates. The reactions of 1-propynyl radical with d4-propyne and propene form products from both hydrogen atom and methyl loss, (–H = 27%, –CH₃ = 73%) and (–H = 14%,more »« less

Authors:

Kirk, Benjamin B. ^[1]; Savee, John D. ^[2]; Trevitt, Adam J. ^[3]; Osborn, David L. ^[2]; Wilson, Kevin R. ^[1]

Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sandia National Lab. (SNL-CA), Livermore, CA (United States)
Univ. of Wollongong (Australia)

Publication Date:: Thu Jul 16 00:00:00 EDT 2015

Research Org.:: Sandia National Lab. (SNL-CA), Livermore, CA (United States)

Sponsoring Org.:: USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:: 1329622

Report Number(s):: SAND-2016-10080J
Journal ID: ISSN 1463-9076; PPCPFQ; 648115

Grant/Contract Number:: AC04-94AL85000

Resource Type:: Accepted Manuscript

Journal Name:: Physical Chemistry Chemical Physics. PCCP (Print)

Additional Journal Information:: Journal Name: Physical Chemistry Chemical Physics. PCCP (Print); Journal Volume: 17; Journal Issue: 32; Journal ID: ISSN 1463-9076

Publisher:: Royal Society of Chemistry

Country of Publication:: United States

Language:: English

Subject:: 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats


                    Kirk, Benjamin B., Savee, John D., Trevitt, Adam J., Osborn, David L., and Wilson, Kevin R. Molecular weight growth in Titan's atmosphere: Branching pathways for the reaction of 1-propynyl radical (H3CC≡C˙) with small alkenes and alkynes.  United States: N. p., 2015. 
Web.  doi:10.1039/c5cp02589c.

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                    Kirk, Benjamin B., Savee, John D., Trevitt, Adam J., Osborn, David L., & Wilson, Kevin R. Molecular weight growth in Titan's atmosphere: Branching pathways for the reaction of 1-propynyl radical (H3CC≡C˙) with small alkenes and alkynes.  United States.  https://doi.org/10.1039/c5cp02589c

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                    Kirk, Benjamin B., Savee, John D., Trevitt, Adam J., Osborn, David L., and Wilson, Kevin R. Thu .  
"Molecular weight growth in Titan's atmosphere: Branching pathways for the reaction of 1-propynyl radical (H3CC≡C˙) with small alkenes and alkynes".  United States.  https://doi.org/10.1039/c5cp02589c.  https://www.osti.gov/servlets/purl/1329622.

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@article{osti_1329622,

  title        = {Molecular weight growth in Titan's atmosphere: Branching pathways for the reaction of 1-propynyl radical (H3CC≡C˙) with small alkenes and alkynes},

  author       = {Kirk, Benjamin B. and Savee, John D. and Trevitt, Adam J. and Osborn, David L. and Wilson, Kevin R.},

  abstractNote = {The reaction of small hydrocarbon radicals (i.e. ˙CN, ˙C2H) with trace alkenes and alkynes is believed to play an important role in molecular weight growth and ultimately the formation of Titan's characteristic haze. Current photochemical models of Titan's atmosphere largely assume hydrogen atom abstraction or unimolecular hydrogen elimination reactions dominate the mechanism, in contrast to recent experiments that reveal significant alkyl radical loss pathways during reaction of ethynyl radical (˙C2H) with alkenes and alkynes. In this study, the trend is explored for the case of a larger ethynyl radical analogue, the 1-propynyl radical (H3CC≡C˙), a likely product from the high-energy photolysis of propyne in Titan's atmosphere. Using synchrotron vacuum ultraviolet photoionization mass spectrometry, product branching ratios are measured for the reactions of 1-propynyl radical with a suite of small alkenes (ethylene and propene) and alkynes (acetylene and d4-propyne) at 4 Torr and 300 K. Reactions of 1-propynyl radical with acetylene and ethylene form single products, identified as penta-1,3-diyne and pent-1-en-3-yne, respectively. These products form by hydrogen atom loss from the radical-adduct intermediates. The reactions of 1-propynyl radical with d4-propyne and propene form products from both hydrogen atom and methyl loss, (–H = 27%, –CH3 = 73%) and (–H = 14%, –CH3 = 86%), respectively. Altogether, these results indicate that reactions of ethynyl radical analogues with alkenes and alkynes form significant quantities of products by alkyl loss channels, suggesting that current photochemical models of Titan over predict both hydrogen atom production as well as the efficiency of molecular weight growth in these reactions.},

  doi          = {10.1039/c5cp02589c},

  journal      = {Physical Chemistry Chemical Physics. PCCP (Print)},

  number       = 32,

  volume       = 17,

  place        = {United States},

  year         = {Thu Jul 16 00:00:00 EDT 2015},

  month        = {Thu Jul 16 00:00:00 EDT 2015}

}

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Title: Molecular weight growth in Titan's atmosphere: Branching pathways for the reaction of 1-propynyl radical (H3CC≡C˙) with small alkenes and alkynes

Abstract

Citation Formats

Title: Molecular weight growth in Titan's atmosphere: Branching pathways for the reaction of 1-propynyl radical (H₃CC≡C˙) with small alkenes and alkynes