TY - JOUR

T1 - NMR and EPR Studies of Free-Radical Intermediates from Experiments Mimicking the Winds on Mars

T2 - A Sink for Methane and Other Gases

AU - Jakobsen, Hans J.

AU - Song, Likai

AU - Gan, Zhehong

AU - Hung, Ivan

AU - Bildsoe, Henrik

AU - Skibsted, Jorgen

AU - Bak, Ebbe N.

AU - Finster, Kai

AU - Nornberg, Per

AU - Jensen, Svend Knak

PY - 2016

Y1 - 2016

N2 - A new kind of solid gas chemical reactions has been investigated using solid-state powder H-2, C-13, and Si-29 NMR and EPR spectroscopies. These studies involve reactions between a silicate-created Si free-radical intermediate and a few ordinary gases such as isotopically H-2-, C-13-, and O-17-enriched methane ((CH4)-C-13 and CD4), carbon dioxide ((CO2)-C-13), hydrogen (H-2(2)) and oxygen (O-17(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 (SiO2) or corundum (alpha-AL(2)O(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 gamma-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. C-13{H-1} and Si-29{H-1} CP/MAS NMR experiments of the reaction product with methane gas show the presence of one -bond CH3-Si equivalent to and HO-Si equivalent to covalent bonds in its structure and that sieving the product leads to a sensitivity enhancement by a factor of similar to 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 (CO2)-C-13, (encapsulation of the gas) and the indication of a congested methyl group in the product from reaction with methane.

AB - A new kind of solid gas chemical reactions has been investigated using solid-state powder H-2, C-13, and Si-29 NMR and EPR spectroscopies. These studies involve reactions between a silicate-created Si free-radical intermediate and a few ordinary gases such as isotopically H-2-, C-13-, and O-17-enriched methane ((CH4)-C-13 and CD4), carbon dioxide ((CO2)-C-13), hydrogen (H-2(2)) and oxygen (O-17(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 (SiO2) or corundum (alpha-AL(2)O(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 gamma-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. C-13{H-1} and Si-29{H-1} CP/MAS NMR experiments of the reaction product with methane gas show the presence of one -bond CH3-Si equivalent to and HO-Si equivalent to covalent bonds in its structure and that sieving the product leads to a sensitivity enhancement by a factor of similar to 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 (CO2)-C-13, (encapsulation of the gas) and the indication of a congested methyl group in the product from reaction with methane.

KW - ELECTRON-SPIN-RESONANCE

KW - GAMMA-IRRADIATED PYREX

KW - TRAPPED-HOLE CENTERS

KW - MAS NMR

KW - MARTIAN ATMOSPHERE

KW - C-13 NMR

KW - ESR

KW - SPECTRA

KW - GLASSES

KW - SOLIDS

U2 - 10.1021/acs.jpcc.6b08847

DO - 10.1021/acs.jpcc.6b08847

M3 - Journal article

VL - 120

SP - 26138

EP - 26149

JO - The Journal of Physical Chemistry Part C

JF - The Journal of Physical Chemistry Part C

SN - 1932-7447

IS - 45

ER -