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Abstract Polyethylene (C2H4)n was compressed to pressures between 10 and 30 GPa in a diamond anvil cell (DAC) and laser heated above 2500 K for approximately one second. This resulted in the chemical decomposition of the polymer into carbon and hydrocarbon reaction products. After quenching to ambient temperature, the decomposition products were measured in the DAC at pressures ranging from ambient to 29 GPa using a combination of x-ray diffraction (XRD) and small angle x-ray scattering (SAXS). XRD identified cubic diamond and methane as the predominant product species with their pressure–volume relationships exhibiting strong correlations to the diamond and methane equations of state. Length scales associated with the diamond products, obtained from SAXS measurements, indicate the formation of nanodiamonds with a radius of gyration between 12 and 35 nm consistent with 32–90 nm diameter spherical particles. These results are in good agreement with the predicted product composition under thermodynamic and chemical equilibrium.

Shock-wave driven reactions of organic molecules may have played a key role in prebiotic chemistry, but their mechanisms are difficult to investigate. The authors, using time-resolved x-ray diffraction and small-angle x-ray scattering experiments, observe the transformation of liquid benzene during a shock, identifying carbon and hydrocarbon solid products.

Femtosecond time-resolved photoelectron spectroscopy and high-level theoretical calculations were used to study the effects of methyl substitution on the electronic dynamics of the ,-enones acrolein (2-propenal), crotonaldehyde (2-butenal), methylvinylketone (3-buten-2-one), and methacrolein (2-methyl-2-propenal) following excitation to the S2() state at 209 and 200 nm. We determine that following excitation the molecules move rapidly away from the Franck−Condon region, reaching a conical intersection promoting relaxation to the S1(n) state. Once on the S1surface, the trajectories access another conical intersection, leading them to the ground state. Only small variations between molecules are seen in their S2decay times. However, the position of methyl group substitution greatly affects the relaxation rate from the S1surface and the branching ratios to the products. Ab initio calculations used to compare the geometries, energies, and topographies of the S1/S0conical intersections of the molecules are not able to satisfactorily explain the variations in relaxation behavior. We propose that the S1lifetime differences are caused by specific dynamical factors that affect the efficiency of passage through the S1/S0conical intersection. [ABSTRACT FROM AUTHOR]