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Ismail, Huzeifa; Franklin Goldsmith, C.; Abel, Paul R.; Howe, Pui T.; Fahr, Askar; Halpern, Joshua B.; Jusinski, Leonard E.; Georgievskii, Yuri; Taatjes, Craig A.; Green, William H.

This work reports measurements of absolute rate coefficients and Rice-Ramsperger-Kassel-Marcus (RRKM) master equation simulations of the C 2H 3 + C 2H 4 reaction. Direct kinetic studies were performed over a temperature range of 300-700 K and pressures of 20 and 133 mbar. Vinyl radicals (H 2C=CH) were generated by laser photolysis of vinyl iodide (C 2H 3I) at 266 nm, and time-resolved absorption spectroscopy was used to probe vinyl radicals through absorption at 423.2 nm. Measurements at 20 mbar are in good agreement with previous determinations at higher temperature. A weighted three-parameter Arrhenius fit to the experimental rate constant at 133 mbar, with the temperature exponent fixed, gives k = (7 ±1) × 10 -14 cm 3 molecule -1 s -1 (T/298 K) 2 exp[-(1430 ± 70) K/T]. RRKM master equation simulations, based on G3 calculations of stationary points on the C 4H 7 potential energy surface, were carried out to predict rate coefficients and product branching fractions. The predicted branching to 1-methylallyl product is relatively small under the conditions of the present experiments but increases as the pressure is lowered. Analysis of end products of 248 nm photolysis of vinyl iodide/ethylene mixtures at total pressures between 27 and 933 mbar provides no direct evidence for participation of 1-methylallyl. © 2007 American Chemical Society.

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TYPE Journal Article YEAR 2007

Scopus OSTI DOI

Kinetic Measurements and Modeling of OH Formation in Alkyl Oxidation

Abel, Paul A.; Jusinski, Leonard E.; Taatjes, Craig A.

Abstract not provided.

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TYPE Presentation YEAR 2007

OSTI

Measurements and Quasi-Quantum Modeling of the Steric Asymmetry and Parity Propensities in State-to-State Rotationally Inelastic Scattering of NO (²Π_1/2) with D₂

Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory

Taatjes, Craig A.

In this paper, relative integrated cross sections are measured for spin-orbit-conserving, rotationally inelastic scattering of NO (²Π_1/2), hexapole-selected in the upper Λ-doublet level of the ground rotational state (j = 0.5), in collisions with D₂ at a nominal energy of 551 cm^-1. The final state of the NO molecule is detected by laser-induced fluorescence (LIF). The state-selected NO molecule is oriented with either the N end or the O end toward the incoming D₂ molecule by application of a static electric field E in the scattering region. This field is directed parallel or antiparallel to the relative velocity vector v. Comparison of signals taken for the different applied field directions gives the experimental steric asymmetry SA, defined by SA = (σ_v↑↓E - σ_v↑↑E)/(σ_v↑↓E + σ_v↑↑E), which is equal to within a factor of -1 to the molecular steric effect, S_i→f ≡ (σ_D₂→NO - σ_D₂→ON)/(σ_D₂→NO + σ_D₂→ON). The dependence of the integral inelastic cross section on the incoming Λ-doublet component is also measured as a function of the final rotational (j_final) and Λ-doublet (ε_final) state. The measured steric asymmetries are similar to those previously observed for NO-He scattering. Spin-orbit manifold-conserving collisions exhibit a larger propensity for parity conservation than their NO-He counterparts. The results are interpreted in the context of the recently developed quasi-quantum treatment (QQT) of rotationally inelastic scattering. The QQT predictions can be inverted to obtain a fitted hard-shell potential that reproduces the experimental steric asymmetry; this fitted potential gives an empirical estimate of the anisotropy of the repulsive interaction between NO and D₂. Finally, QQT computation of the differential cross section using this simple model potential shows reasonable agreement with the measured differential cross sections.