Q-band esr spectra of?-irradiated Pyrex

Dynamic Solid-State NMR Experiments Reveal Structural Changes for a Methyl Silicate Nanostructure on Deuterium Substitution

“…The solid-state Si free-radical intermediate and its gas-reaction silicate products are formed in a newly designed, slow-rotating apparatus which by mechanical tumbling of Pyrex glass flasks (containing abrasive particles and gases) mimics the winds and collision speed of the mineral particles on Mars. , These recent NMR and EPR results prove that abrasive effects of hard materials (e.g., SiO 2 /quartz or α-Al 2 O 3 /corundum grains) on softer Si-containing glasses (e.g., Pyrex and quartz glasses) produce free radicals with unpaired electrons residing on the silicon atoms. In addition, our recent EPR results also show that these free radicals are identical to the proposed free-radical submicroscopic silicate structure (today named “silicate nanomaterial”) observed from γ-irradiation of Pyrex and quartz glasses, − however, of unknown chemical structure. Ever since these very early EPR proposals of either small chains or helices for the structure of the free radical silicate nanomaterial, − apparently no new conclusive structural information has been obtained for the radical or for the gas reaction products, as produced and recently investigated .…”

“…In addition, our recent EPR results also show that these free radicals are identical to the proposed free-radical submicroscopic silicate structure (today named “silicate nanomaterial”) observed from γ-irradiation of Pyrex and quartz glasses, − however, of unknown chemical structure. Ever since these very early EPR proposals of either small chains or helices for the structure of the free radical silicate nanomaterial, − apparently no new conclusive structural information has been obtained for the radical or for the gas reaction products, as produced and recently investigated . The many years of ongoing dispute among Mars researchers on the reasons for the apparently rapid disappearance and reappearance of methane on Mars (e.g., at the Gale crater by the Curiosity team , ) has provoked an intense solid-state NMR structural investigation by our solid-state NMR group on the reaction products following reaction of the radical (or possibly through further intermediate stages) with methane.…”

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

“…This spectrum exhibits the same very sharp and intense resonance at g = 2.0005 similar to that observed for Sample 0 (Figure 10), which is also identical to the trappedelectron resonance first observed in irradiated silica glass by Weeks. 25 The work by Silsbee 27 indicated that the unpaired electron is trapped on a silicon atom while the investigations by Brown 20,21 contribute to the characterization of this resonance also observed in γ-irradiated Pyrex borosilicate glass. Figure 13b shows that increasing the microwave power to 40 mW leads to the appearance of a broadened resonance and partial saturation of the narrow resonance similar to the corresponding observation for Sample 0 in Figure 10.…”

“…The spectra contain a very sharp peak observed at g = 2.0006 at low (0.2 mW) microwave power and a broadened spectrum at high (40 mW) microwave power, resulting in an overlap between the sharp peak and a broadened multiplet resonance. The spectra are similar to the EPR spectra investigated by Brown 20,21 on γ-irradiation of commercial Pyrex glass. The only difference between the spectra shown in Figure 10 of this work and those in Figures 1 and 2 of Brown's study 20 is the much higher concentration of the radical producing the narrow peak in our sample as compared to Brown's sample.…”

“…As shown in this research, the EPR spectra in Figure 10 for our original tumbled 1 Sample 0 are identical to the corresponding EPR spectra presented by Brown in Figures 1 and 2 of ref 20, which were obtained from γ-irradiated Pyrex− borosilicate glass rods. According to the studies by Brown, 20,21 the single sharp resonance at g = 2.0006 ± 0.0002 does not arise from the borosilicate structure but from a submicroscopic structure existing as helices or chains of SiO4 tetrahedra. These observations by Brown are supported by the EPR spectrum of Sample 1 (i.e., the <100 μm sieved fraction of Sample 0) shown in Figure 11a and the EPR spectrum in Figure 12 for Sample 2 (<250 μm sieved fraction)the α-Al 2 O 3 (corundum) sample.…”