Melanie White

Communication: A novel method for generating molecular mixtures at extreme conditions: The case of hydrogen and oxygen

We have successfully created a segregated mixture of hydrogen and oxygen at high pressure in a diamond anvil cell using hard x-ray photochemistry. A keyhole (two holes connected by an opening) sample chamber was created in a metallic gasket to support two segregated powders of ammonia borane and potassium perchlorate, respectively, in each hole at a pressure of ~5.0 GPa. Both holes were separately irradiated with synchrotron hard x-rays to release molecular oxygen and molecular hydrogen, respectively. Upon irradiation of the first KClO4-containing hole, solid reddish-orange O2 appeared in the region of irradiation and molecular oxygen was found to diffuse throughout the entire sample region. The second ammonia borane-containing hole was then irradiated and H2 was observed to form via Raman spectroscopy. Water also was observed in the ammonia borane-containing hole and possibly (in the form of ice VII) in the second hole. This unique experiment demonstrates the ability to easily create solid mixtures of simple molecular systems via x-ray irradiation and then react them via further irradiation which will aid the study of chemistry under extreme conditions.

A Novel Method for Generating Molecular Mixtures at Extreme Conditions: The Case of Fluorine and Oxygen

We have successfully created a segregated mixture of molecular fluorine and oxygen at high pressure in a diamond anvil cell (DAC) via useful hard x-ray photochemistry. A keyhole-like sample chamber was created in a stainless steel gasket to hold two segregated powders of potassium tetrafluoroborate (KBF4) and potassium perchlorate (KClO4) respectively in each hole at a pressure of ∼3.0 GPa. Both holes were individually irradiated with synchrotron hard x-rays to release molecular fluorine and molecular oxygen, respectively. Upon irradiation of the hole containing KBF4 molecular fluorine appeared (as evidenced via Raman spectroscopy) near the region of irradiation. The second hole containing KClO4 was then irradiated and reddish-orange O2 was observed to form. Oxygen was observed to diffuse throughout both holes. There is some evidence that oxygen difluoride (OF2) was formed in the hole originally containing the KBF4.

Hexafluorobenzene under Extreme Conditions

We report the results from three high pressure experiments on hexafluorobenzene (C6F6). In the first experiment, Raman spectra were recorded up to 34.4 GPa. A phase transition from I → II was observed near 2 GPa. Near 8.8 GPa, a phase transition to an unreported phase (III) commenced. Above 20.6 GPa, yet another phase was observed (IV). Pressure cycling was employed to determine that, below 25.6 GPa, all pressure-induced alterations were reversible. However, at pressures above 20 GPa, dramatic spectral changes and broadening were observed at 25.6 and 34.4 GPa. The sample irreversibly changed into a soft solid with waxlike consistency when pressure was reduced to ambient and was recoverable. In the second experiment, IR spectra were collected up to 14.6 GPa. The phase transition (II → III) near 8.8 GPa was confirmed. An angular dispersive X-ray diffraction experiment was conducted to 25.6 GPa. Phase transitions above 1.4 GPa (I → II), above 5.5 GPa (II → III), above 10 GPa (III → IV), and above 15.5 GPa (IV → V) were observed. Near 25.6 GPa, long-range crystalline order was lost as the X-ray diffraction spectrum presented evidence of an amorphous solid.

A novel synthesis of polymeric CO via useful hard x-ray photochemistry

Abstract We report on the synchrotron hard X-ray-induced decomposition of strontium oxalate (SrC2O4) pressurized to 7 GPa inside a diamond anvil cell (DAC). After some 4 h of irradiation in a white X-ray synchrotron beam, a dark reddish/brown region formed in the area of irradiation which was surrounded by a yellowish brown remainder in the rest of the sample. Upon depressurization of the sample to ambient conditions, the reacted/decomposed sample was recoverable as a dark brown/red and yellow waxy solid. Synchrotron infrared spectroscopy confirmed the strong presence of CO2 even under ambient conditions with the sample exposed to air and other strongly absorbing regions, suggesting that the sample may likely be polymerized CO (in part) with dispersed CO2 and SrO trapped within the polymer. These results will have significant implications in the ability to readily produce and trap CO2 in situ via irradiation of a simple powder for useful hard X-ray photochemistry and in the ability to easily manufacture polymeric CO (via loading of powders in a DAC or high volume press) without the need for the dangerous and complex loading of toxic CO. A novel means of X-ray-induced polymerization under extreme conditions has also been demonstrated.

Forcing Cesium into Higher Oxidation States Using Useful hard x-ray Induced Chemistry under High Pressure

This paper discusses our attempt to synthesize higher oxidation forms of cesium fluoride by pressurizing cesium fluoride in a fluorine-rich environment created via the x-ray decomposition of potassium tetrafluoroborate. This was done in order to confirm recent theoretical predictions of higher oxidation forms of CsFn. We discuss the development of a technique to produce molecular fluorine in situ via useful hard x-ray photochemistry, and the attempt to utilize this technique to form higher oxidation states of cesium fluoride. In order to verify the formation of the novel stoichiometric species of CsFn. X-ray Absorption Near Edge Spectroscopy (XANES) centered on the cesium K-edge was performed to probe the oxidation state of cesium as well as the local molecular coordination around Cs.