Bulletin of the American Physical Society
18th Biennial Intl. Conference of the APS Topical Group on Shock Compression of Condensed Matter held in conjunction with the 24th Biennial Intl. Conference of the Intl. Association for the Advancement of High Pressure Science and Technology (AIRAPT)
Volume 58, Number 7
Sunday–Friday, July 7–12, 2013; Seattle, Washington
Session V7: CH.2 Chemistry: Optical Initiation |
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Chair: Brian Jensen, Los Alamos National Laboratory Room: Grand Crescent |
Thursday, July 11, 2013 1:45PM - 2:15PM |
V7.00001: Non-linear optical techniques and optical properties of condensed molecular systems Invited Speaker: Margherita Citroni Structure, dynamics, and optical properties of molecular systems can be largely modified by the applied pressure, with remarkable consequences on their chemical stability. Several examples of selective reactions yielding technologically attractive products can be cited, which are particularly efficient when photochemical effects are exploited in conjunction with the structural conditions attained at high density. Non-linear optical techniques are a basic tool to unveil key aspects of the chemical reactivity and dynamic properties of molecules. Their application to high-pressure samples is experimentally challenging, mainly because of the small sample dimensions and of the non-linear effects generated in the anvil materials. In this talk I will present results on the electronic spectra of several aromatic crystals obtained through two-photon induced fluorescence and two-photon excitation profiles measured as a function of pressure (typically up to about 25 GPa), and discuss the relationship between the pressure-induced modifications of the electronic structure and the chemical reactivity at high pressure. I will also present the first successful pump-probe infrared measurement performed as a function of pressure on a condensed molecular system. The system under examination is liquid water, in a sapphire anvil cell, up to 1 GPa along isotherms at 298 and 363 K. These measurements give a new enlightening insight into the dynamical properties of low- and high-density water allowing a definition of the two structures. [Preview Abstract] |
Thursday, July 11, 2013 2:15PM - 2:30PM |
V7.00002: High pressure chemistry of red phosphorus by photoactivated simple molecules Matteo Ceppatelli, Roberto Bini, Samuele Fanetti, Maria Caporali, Maurizio Peruzzini High pressure (HP) is very effective in reducing intermolecular distances and inducing unexpected chemical reactions. In particular the photoactivation of the reactants in HP conditions can lead to very efficient and selective processes. The chemistry of phosphorus is currently based on the white molecular form. The red polymeric allotrope, despite more stable and much less toxic, has not attracted much attention so far. However, switching from the white to the red form would benefit any industrial procedure, especially from an environmental point of view. On the other side, water and ethanol are renewable, environmental friendly and largely available molecules, usable as reactants and photoactivators in HP conditions. Here we report a study on the HP photoinduced reactivity of red phosphorus with water and ethanol, showing the possibility of very efficient and selective processes, leading to molecular hydrogen and valuable phosphorus compounds. The reactions have been studied by means of FTIR and Raman spectroscopy and pressure has been generated using DAC and SAC. HP reactivity has been activated by the two-photon absorption of near-UV wavelengths and occured in total absence of solvents, catalysts and radical initiators, at room T and mild pressure conditions (0.2-1.5 GPa). [Preview Abstract] |
Thursday, July 11, 2013 2:30PM - 2:45PM |
V7.00003: Studies in useful hard x-ray induced chemistry Michael Pravica, Ligang Bai, Daniel Sneed, Changyong Park The observed rapid decomposition of potassium chlorate (via 2KClO$_{3}+$ h$\nu \to $ 2KCl $+$3O$_{2})$ via synchrotron hard x-ray irradiation (\textgreater 10 keV) has enabled experiments that are developing novel and useful hard x-ray chemistry. We have observed a number of radiation-induced \textit{in situ} decomposition reactions in various substances which release O$_{2}$, H$_{2}$, N$_{2}$, NH$_{3}$, and H$_{2}$O in a diamond anvil cell (DAC) at ambient and high pressures. These novel acatalytic and isothermal reactions represent a highly controllable, penetrating, and focused method to initiate chemistry (including x-ray induced combustion) in sealed and/or isolated chambers which maintain matter under extreme conditions. During our studies, we have typically observed a slowing of decomposition with pressure including phase dependent decomposition of KClO$_{3}$. Energy dependent studies have observed an apparent resonance near 15 keV at which the decomposition rate is maximized. This may enable use of much lower flux and portable x-ray sources (e.g. x-ray tubes) in larger scale experiments . These developments support novel means to load DACs and control chemical reactions providing novel routes of synthesis of novel materials under extreme conditions. [Preview Abstract] |
Thursday, July 11, 2013 2:45PM - 3:00PM |
V7.00004: Structural characterization of high-pressure liquid water by transient infrared ultrafast spectroscopy Samuele Fanetti, Andrea Lapini, Marco Pagliai, Margherita Citroni, Mariangela Di Donato, Sandro Scandolo, Roberto Righini, Roberto Bini Experimental and computational studies have reported in the last years the existence of two different local structures of liquid water depending on pressure and temperature conditions, called low density (LDW) and high density water (HDW). For the first time we have combined pump-probe ultrafast spectroscopy with ultra high pressure devices to access the gigapascal range, providing new insights on the understanding of the two structures peculiarities and their interconversion, in the whole range of thermodynamic stability of liquid water, from 273 to 363 K, from ambient pressure up to 1.2 GPa. We measured the OD stretching rotational anisotropy decay time-constant and vibrational lifetime T1, in a solution of HOD in H2O, pressurized in a sapphire anvil cell, as a function of pressure at different temperatures and we performed a careful infrared linewidth study of the OD stretching mode as a function of temperature and pressure. We interpreted the pressure evolution of the measured parameters in terms of structural changes, identifying the key to correlate the structure evolution with the dynamic data that led us to define the pressure and temperature region where only HDW exists. [Preview Abstract] |
Thursday, July 11, 2013 3:00PM - 3:15PM |
V7.00005: Transient Absorption and Hugoniot Equations of State of Shocked Reactive Liquids Kathryn Brown, Shawn McGrane, Peter Schulze, Nhan Dang, David Moore We use transient absorption spectroscopy and ultrafast dynamic ellipsometry (UDE) to characterize reactions that occur in reactive liquid thin layers, including nitromethane and carbon disulfide, that have been subjected to sustained ($\sim$300 ps) shocks up to \textless 20 GPa from an amplified Ti:sapphire laser. Shock compression can cause some liquids to react and form new chemical species. Though not chemical-specific, transient absorption and deviations from the universal liquid Hugoniot can indicate the presence of chemical reactions taking place. The information obtained from these experiments can be applied to more specific characterization methods such as vibrational spectroscopy. [Preview Abstract] |
Thursday, July 11, 2013 3:15PM - 3:30PM |
V7.00006: Transformation of Simple Molecular Fluids to Conducting States in the Laser-Heated Diamond Anvil Cell R.S. McWilliams, D.A. Dalton, M.F. Mahmood, A.F. Goncharov The nature of high-pressure, high-temperature chemical and electronic transformation of simple molecular materials such as hydrogen and nitrogen is a subject of ongoing study and many open questions. Particularly challenging is the laboratory study of states corresponding with fluid-fluid phase transformations, from insulator to conductor and/or molecular to non-molecular. These may take the form of first-order (i.e. discontinuous in P and T) phase boundaries at conditions yet to be explored completely by experiments. Previously, such states were accessible solely via dynamic compression techniques, however limitations in experimental geometry and timescale and confinement to adiabatic pathways has limited the range of conditions accessed and the variety of measurements available. New developments in static compression, involving the acceleration of laser-heated diamond-anvil-cell experiments to microsecond timescales via fast spectroscopy, enable study of this interesting regime in hydrogen and nitrogen as well as novel measurements of material state. These results complement dynamic compression data and extend measurements to previously unexplored conditions where first-order liquid-liquid transformations have been predicted. [Preview Abstract] |
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