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 (13CO2), hydrogen
(2H2), and oxygen (17O2). 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 (α-Al2O3) 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 γ-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 13CO2 (encapsulation
of the gas) and the indication of a congested methyl group in the
product from reaction with methane.
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