Pressure-Dependent I‑Atom Yield in the Reaction of CH₂I with O₂ Shows a Remarkable Apparent Third-Body Efficiency for O₂

The formation of I atom and Criegee intermediate (CH₂OO) in the reaction of CH₂I with O₂ has potential relevance for aerosol and organic acid production in the marine boundary layer. We report measurements of the absolute yield of I atom as a function of pressure for N₂, He, and O₂ buffer at 298 K. Although the overall rate coefficient is pressure-independent, the I-atom yield, correlated with CH₂OO, decreases with total pressure, presumably because of increased stabilization of CH₂IOO. The extrapolated yield of the I + Criegee channel under tropospheric conditions is small but nonzero, ∼0.04. The zero-pressure limiting I-atom yield is unity, within experimental error, implying negligible branching to IO + CH₂O. The apparent collision efficiency of O₂ in stabilizing CH₂IOO is a remarkable factor of 13 larger than that of N₂, which suggests unusually strong interaction or possible reaction between the chemically activated CH₂IOO^# and O₂

Additional file 1: of Comparison of the complications of traditional 12 cores transrectal prostate biopsy with image fusion guided transperineal prostate biopsy

Multiparametric MRI Examination and Analysis. (DOCX 14 kb

Effect of Carbon Supports on Pd Catalyst for Hydrogenation Debenzylation of Hexabenzylhexaazaisowurtzitane (HBIW)

<p>A series of carbon material–supported Pd catalysts was prepared and used for hydrogenation debenzylation of hexabenzylhexaazaisowurtzitane (HBIW). The structures and morphologies of carbon supports were characterized by field emission scanning electron microscopy (FESEM), physical adsorption, and Raman spectroscopy. X-ray diffraction (XRD), H₂-TPR, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) were used to characterize Pd-supported carbon. The species Pd, with the states, Pd° and PdOx, were presented to the catalysts and can be reduced to Pd° as the active centers during the reaction. Among layer, tube, and ordered/disordered pore structures, disordered mesoporous carbon exhibited a high content of Pd on the surface and can be used as an efficient support in terms of high catalytic activity and good recycled stability for hydrogenation debenzylation of HBIW.</p

Multiscale Informatics for Low-Temperature Propane Oxidation: Further Complexities in Studies of Complex Reactions

The present paper describes further development of the multiscale informatics approach to kinetic model formulation of Burke et al. (Burke, M. P.; Klippenstein, S. J.; Harding, L. B. <i>Proc. Combust. Inst.</i> <b>2013</b>, <i>34</i>, 547–555) that directly incorporates elementary kinetic theories as a means to provide reliable, physics-based extrapolation of kinetic models to unexplored conditions. Here, we extend and generalize the multiscale informatics strategy to treat systems of considerable complexityinvolving multiwell reactions, potentially missing reactions, nonstatistical product branching ratios, and non-Boltzmann (i.e., nonthermal) reactant distributions. The methodology is demonstrated here for a subsystem of low-temperature propane oxidation, as a representative system for low-temperature fuel oxidation. A multiscale model is assembled and informed by a wide variety of targets that include <i>ab initio</i> calculations of molecular properties, rate constant measurements of isolated reactions, and complex systems measurements. Active model parameters are chosen to accommodate both “parametric” and “structural” uncertainties. Theoretical parameters (e.g., barrier heights) are included as active model parameters to account for parametric uncertainties in the theoretical treatment; experimental parameters (e.g., initial temperatures) are included to account for parametric uncertainties in the physical models of the experiments. RMG software is used to assess potential structural uncertainties due to missing reactions. Additionally, branching ratios among product channels are included as active model parameters to account for structural uncertainties related to difficulties in modeling sequences of multiple chemically activated steps. The approach is demonstrated here for interpreting time-resolved measurements of OH, HO₂, <i>n</i>-propyl, <i>i</i>-propyl, propene, oxetane, and methyloxirane from photolysis-initiated low-temperature oxidation of propane at pressures from 4 to 60 Torr and temperatures from 300 to 700 K. In particular, the multiscale informed model provides a consistent quantitative explanation of both <i>ab initio</i> calculations and time-resolved species measurements. The present results show that interpretations of OH measurements are significantly more complicated than previously thoughtin addition to barrier heights for key transition states considered previously, OH profiles also depend on additional theoretical parameters for R + O₂ reactions, secondary reactions, QOOH + O₂ reactions, and treatment of non-Boltzmann reaction sequences. Extraction of physically rigorous information from those measurements may require more sophisticated treatment of all of those model aspects, as well as additional experimental data under more conditions, to discriminate among possible interpretations and ensure model reliability

Direct Measurements of Unimolecular and Bimolecular Reaction Kinetics of the Criegee Intermediate (CH₃)₂COO

The Criegee intermediate acetone oxide, (CH₃)₂COO, is formed by laser photolysis of 2,2-diiodopropane in the presence of O₂ and characterized by synchrotron photoionization mass spectrometry and by cavity ring-down ultraviolet absorption spectroscopy. The rate coefficient of the reaction of the Criegee intermediate with SO₂ was measured using photoionization mass spectrometry and pseudo-first-order methods to be (7.3 ± 0.5) × 10^–11 cm³ s^–1 at 298 K and 4 Torr and (1.5 ± 0.5) × 10^–10 cm³ s^–1 at 298 K and 10 Torr (He buffer). These values are similar to directly measured rate coefficients of <i>anti</i>-CH₃CHOO with SO₂, and in good agreement with recent UV absorption measurements. The measurement of this reaction at 293 K and slightly higher pressures (between 10 and 100 Torr) in N₂ from cavity ring-down decay of the ultraviolet absorption of (CH₃)₂COO yielded even larger rate coefficients, in the range (1.84 ± 0.12) × 10^–10 to (2.29 ± 0.08) × 10^–10 cm³ s^–1. Photoionization mass spectrometry measurements with deuterated acetone oxide at 4 Torr show an inverse deuterium kinetic isotope effect, <i>k</i>_H/<i>k</i>_D = (0.53 ± 0.06), for reactions with SO₂, which may be consistent with recent suggestions that the formation of an association complex affects the rate coefficient. The reaction of (CD₃)₂COO with NO₂ has a rate coefficient at 298 K and 4 Torr of (2.1 ± 0.5) × 10^–12 cm³ s^–1 (measured with photoionization mass spectrometry), again similar to rate for the reaction of <i>anti</i>-CH₃CHOO with NO₂. Cavity ring-down measurements of the acetone oxide removal without added reagents display a combination of first- and second-order decay kinetics, which can be deconvolved to derive values for both the self-reaction of (CH₃)₂COO and its unimolecular thermal decay. The inferred unimolecular decay rate coefficient at 293 K, (305 ± 70) s^–1, is similar to determinations from ozonolysis. The present measurements confirm the large rate coefficient for reaction of (CH₃)₂COO with SO₂ and the small rate coefficient for its reaction with water. Product measurements of the reactions of (CH₃)₂COO with NO₂ and with SO₂ suggest that these reactions may facilitate isomerization to 2-hydroperoxypropene, possibly by subsequent reactions of association products