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Title: Tabletop Femtosecond VUV Photoionization and PEPICO Detection of Microreactor Pyrolysis Products

Abstract

Here, we report the combination of tabletop vacuum ultraviolet photoionization with photoion--photoelectron coincidence spectroscopy for sensitive, isomer-specific detection of nascent products from a pyrolysis microreactor. Results on several molecules demonstrate two essential capabilities that are very straightforward to implement: the ability to differentiate isomers, and to distinguish thermal products from dissociative ionization. We derive vacuum ultraviolet light is from a commercial tabletop femtosecond laser system, allowing data to be collected at 10 kHz; this high repetition rate is critical for coincidence techniques. The photoion—photoelectron coincidence spectrometer uses the momentum of the ion to identify dissociative ionization events, and coincidence techniques to provide a photoelectron spectrum specific to each mass, which is used to distinguish different isomers. We also have used this spectrometer to detect the pyrolysis products that result from the thermal cracking of acetaldehyde, cyclohexene, and 2-butanol. The photoion—photoelectron spectrometer can detect and identify organic radicals and reactive intermediates that result from pyrolysis. Direct comparison of laboratory and synchrotron data illustrate the advantages and potential of this approach.

Authors:
ORCiD logo [1];  [2];  [2];  [2];  [1]; ORCiD logo [2];  [1];  [1]; ORCiD logo [1]
  1. Univ. of Colorado, Boulder, CO (United States). JILA and Dept. of Physics
  2. Univ. of Colorado, Boulder, CO (United States). Dept. of Chemistry
Publication Date:
Research Org.:
Univ. of Colorado, Boulder, CO (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1372114
Grant/Contract Number:
FG02-99ER14982; AC02-05CH11231; CBET-1403979
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory
Additional Journal Information:
Journal Volume: 121; Journal Issue: 28; Journal ID: ISSN 1089-5639
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS

Citation Formats

Couch, David E., Buckingham, Grant T., Baraban, Joshua H., Porterfield, Jessica P., Wooldridge, Laura A., Ellison, G. Barney, Kapteyn, Henry C., Murnane, Margaret M., and Peters, William K.. Tabletop Femtosecond VUV Photoionization and PEPICO Detection of Microreactor Pyrolysis Products. United States: N. p., 2017. Web. doi:10.1021/acs.jpca.7b02821.
Couch, David E., Buckingham, Grant T., Baraban, Joshua H., Porterfield, Jessica P., Wooldridge, Laura A., Ellison, G. Barney, Kapteyn, Henry C., Murnane, Margaret M., & Peters, William K.. Tabletop Femtosecond VUV Photoionization and PEPICO Detection of Microreactor Pyrolysis Products. United States. doi:10.1021/acs.jpca.7b02821.
Couch, David E., Buckingham, Grant T., Baraban, Joshua H., Porterfield, Jessica P., Wooldridge, Laura A., Ellison, G. Barney, Kapteyn, Henry C., Murnane, Margaret M., and Peters, William K.. Thu . "Tabletop Femtosecond VUV Photoionization and PEPICO Detection of Microreactor Pyrolysis Products". United States. doi:10.1021/acs.jpca.7b02821.
@article{osti_1372114,
title = {Tabletop Femtosecond VUV Photoionization and PEPICO Detection of Microreactor Pyrolysis Products},
author = {Couch, David E. and Buckingham, Grant T. and Baraban, Joshua H. and Porterfield, Jessica P. and Wooldridge, Laura A. and Ellison, G. Barney and Kapteyn, Henry C. and Murnane, Margaret M. and Peters, William K.},
abstractNote = {Here, we report the combination of tabletop vacuum ultraviolet photoionization with photoion--photoelectron coincidence spectroscopy for sensitive, isomer-specific detection of nascent products from a pyrolysis microreactor. Results on several molecules demonstrate two essential capabilities that are very straightforward to implement: the ability to differentiate isomers, and to distinguish thermal products from dissociative ionization. We derive vacuum ultraviolet light is from a commercial tabletop femtosecond laser system, allowing data to be collected at 10 kHz; this high repetition rate is critical for coincidence techniques. The photoion—photoelectron coincidence spectrometer uses the momentum of the ion to identify dissociative ionization events, and coincidence techniques to provide a photoelectron spectrum specific to each mass, which is used to distinguish different isomers. We also have used this spectrometer to detect the pyrolysis products that result from the thermal cracking of acetaldehyde, cyclohexene, and 2-butanol. The photoion—photoelectron spectrometer can detect and identify organic radicals and reactive intermediates that result from pyrolysis. Direct comparison of laboratory and synchrotron data illustrate the advantages and potential of this approach.},
doi = {10.1021/acs.jpca.7b02821},
journal = {Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory},
number = 28,
volume = 121,
place = {United States},
year = {Thu Jun 29 00:00:00 EDT 2017},
month = {Thu Jun 29 00:00:00 EDT 2017}
}

Journal Article:
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  • No abstract prepared.
  • An experimental study of toluene pyrolysis (1.24 vol.% toluene in argon) was performed at low pressure (1.33 kPa) in the temperature range of 1200-1800 K. The pyrolysis process was detected with the tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular-beam mass spectrometry (MBMS). Species up to m/z = 202 (C{sub 16}H{sub 10}), containing many radicals (CH{sub 3}, C{sub 3}H{sub 3}, C{sub 5}H{sub 3}, C{sub 5}H{sub 5}, C{sub 7}H{sub 5}, C{sub 7}H{sub 7}, C{sub 9}H{sub 7}, C{sub 11}H{sub 7} and C{sub 13}H{sub 9}) and isomers, such as C{sub 3}H{sub 4} (propyne and allene), C{sub 4}H{sub 4} (vinylacetylene and 1,2,3-butatriene), C{sub 5}H{submore » 5} (cyclopentadienyl radical and pent-1-en-4-yn-3-yl radical), C{sub 6}H{sub 4} (3-hexene-1,5-diyne and benzyne), C{sub 6}H{sub 6} (benzene and fulvene), C{sub 7}H{sub 8} (toluene and 5-methylene-1,3-cyclohexadiene) and so on, were identified from near-threshold measurements of photoionization mass spectra, and the mole fraction profiles of the pyrolysis products were evaluated from measurements of temperature scan. Experimental results indicate that the reaction C{sub 7}H{sub 8} {yields} C{sub 7}H{sub 7} and the subsequent reactions are dominant at comparatively low temperature (<1440 K), while the reaction C{sub 7}H{sub 8} {yields} C{sub 6}H{sub 5} and subsequent reactions gradually become competitive and important with increasing temperature. Furthermore the barriers of the decomposition pathways of toluene and benzyl radical determined by quantum mechanical calculation are in good agreement with the initial formation temperatures of the species. Based on the mole fractions and formation temperatures of the detected pyrolysis species, a simple reaction network is deduced. At relatively high temperatures, H-abstraction is prevalent and the mole fraction of C{sub 2}H{sub 2} is so high that many aromatics are formed through the hydrogen-abstraction/C{sub 2}H{sub 2}-addition (HACA) mechanism. Moreover the reactions of benzyl with toluene/benzyl/phenyl/propargyl radicals to directly produce larger aromatics should play an influential role in PAH formation. Meanwhile the five-member-ring recombination mechanism also plays an indispensable role in the aromatics growth, as cyclopentadienyl radical (C{sub 5}H{sub 5}) was determined to be a major product of the decomposition of toluene. (author)« less
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