NMR and EPR Studies of Free-Radical Intermediates from Experiments Mimicking the Winds on Mars: A Sink for Methane and Other Gases

Hans J. Jakobsen*, Likai Song, Zhehong Gan, Ivan Hung, Henrik Bildsoe, Jorgen Skibsted, Ebbe N. Bak, Kai Finster, Per Nornberg, Svend Knak Jensen

*Corresponding author for this work

Research output: Contribution to journal/Conference contribution in journal/Contribution to newspaperJournal articleResearchpeer-review

Abstract

A new kind of solid-gas chemical reactions has been investigated using solid-state powder 2H, 13C, and 29Si NMR and EPR spectroscopies. These studies involve reactions between a silicate-created Si free-radical intermediate and a few ordinary gases such as isotopically 2H-, 13C-, and 17O-enriched methane (13CH4 and CD4), carbon dioxide (13CO 2), hydrogen (2H 2), and oxygen (17O 2). The solid-state Si free-radical intermediate and gas reaction and silicate products are formed in a specially designed rotating apparatus, which by mechanical tumbling mimics the winds and collision speed of the mineral particles on Mars. It is shown that the "hard" quartz (SiO 2) or corundum (a-Al2O 3) grain particles, used to simulate the collision particles in a rotating Pyrex (borosilicate) reaction flask, act as an abrasive on the "soft" Pyrex flask and thereby create a silicate Si free-radical intermediate. EPR studies show that this radical is identical to the silicate radical intensively investigated by EPR from ?- irradiation of Pyrex and other glasses and shown to constitute a submicrostructure of either silicate chains or helices. The intensity of the silicate Si free-radical EPR signal for the reaction product is strongly reduced or even disappears by performing the tumbling of the abrasive grain particles in an atmosphere of methane or other gases. 13C{1H} and 29Si{1H} CP/MAS NMR experiments of the reaction product with methane gas show the presence of one-bond CH3-Si= and HO-Si= covalent bonds in its structure and that sieving the product leads to a sensitivity enhancement by a factor of 25. A flexible helical structure for the silicate Si free-radical intermediate is indicated by the preliminary results for the product resulting from the reaction with 13CO 2 (encapsulation of the gas) and the indication of a congested methyl group in the product from reaction with methane.

Original languageEnglish
JournalThe Journal of Physical Chemistry Part C
Volume120
Issue45
Pages (from-to)26138-26149
Number of pages12
ISSN1932-7447
DOIs
Publication statusPublished - 2016

Keywords

  • ELECTRON-SPIN-RESONANCE
  • GAMMA-IRRADIATED PYREX
  • TRAPPED-HOLE CENTERS
  • MAS NMR
  • MARTIAN ATMOSPHERE
  • C-13 NMR
  • ESR
  • SPECTRA
  • GLASSES
  • SOLIDS

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