Binary Diffusion Coefficients for Methane and Fluoromethanes in Nitrogen.

Binary gas-phase diffusion coefficients, of interest in physical models of atmospheric and combustion chemistry, have been measured in for the homologous series of refrigerant-related (fluoro)methanes: methane (), fluoromethane (), difluoromethane (), and trifluoromethane (). Values have been determined by reverse-flow gas chromatography, which has been previously demonstrated to provide accurate results over a wide range of temperatures. Coefficients were measured at temperatures of (300 to 550) K for all species and extending up to 650 K and 723 K for and , respectively, and down to 250 K for .

Diaphragmless single-pulse shock tube for high-temperature chemical kinetics studies.

Single-pulse shock tubes are effective tools for measuring chemical kinetics at high temperatures, typically (900-1400) K. However, the use of a diaphragm for shock generation leads to significant shock-to-shock inconsistencies in temperature for a constant initial pressure ratio across the discontinuity. Diaphragms also require replacement after each shock and demand care in cleaning to ensure that the fragments do not contaminate the apparatus.

Theory and Experiment of Binary Diffusion Coefficient of n-Alkanes in Dilute Gases.

Binary diffusion coefficients were measured for n-pentane, n-hexane, and n-octane in helium and of n-pentane in nitrogen over the temperature range of 300 to 600 K, using reversed-flow gas chromatography. A generalized, analytical theory is proposed for the binary diffusion coefficients of long-chain molecules in simple diluent gases, taking advantage of a recently developed gas-kinetic theory of the transport properties of nanoslender bodies in dilute free-molecular flows. The theory addresses the long-standing question about the applicability of the Chapman-Enskog theory in describing the transport properties of nonspherical molecular structures, or equivalently, the use of isotropic potentials of interaction for a roughly cylindrical molecular structure such as large normal alkanes.

Quantitative evidence for organic peroxy radical photochemistry at 254 nm.

Quantitative evidence is presented for the importance of alkyl peroxy photochemistry in the formation of secondary organic aerosol at 254 nm. Particles were generated by extensively oxidizing dodecanoic acid with photolytically generated hydroxyl radicals in a flow cell. The resulting particles were collected and analyzed for composition, which shows a lower contribution from multiply substituted parent molecules and much more decomposition product than expected from typical low-NOx oxidation mechanisms.

Alkylperoxy radical photochemistry in organic aerosol formation processes.

Recent studies have shown that 254 nm light can be used to generate organic aerosol from iodoalkane/air mixtures via photodissociation of the C-I bond and subsequent oxidation of the alkyl radical. We examine organic aerosol formed from the 1-iodooctane photolysis at this wavelength using high-performance liquid chromatography (HPLC) with derivatization to selectively probe carbonyl- and hydroxyl-containing molecules. Tandem mass spectrometry reveals that the product distributions are much more complex than a traditional low-NOx peroxy-peroxy oxidation mechanism from a single parent isomer would justify.