Yields of HONO and HOONO Products from the Reaction of HO and NO Using Pulsed Laser Photolysis and Mid-Infrared Cavity-Ringdown Spectroscopy.

The reaction of HO with NO is one of the most important steps in radical cycling throughout the stratosphere and troposphere. Previous literature experimental work revealed a small yield of nitric acid (HONO) directly from HO + NO. Atmospheric models previously treated HO + NO as radical recycling, but inclusion of this terminating step had large effects on atmospheric oxidative capacity and the concentrations of HONO and ozone (O), among others.

Evaluated Site-Specific Rate Constants for Reaction of Isobutane with H and CH: Shock Tube Experiments Combined with Bayesian Model Optimization.

Evaluated site-specific rate constants for the reactions of isobutane with CH and H were determined in a combined analysis of new shock tube experiments and existing literature data. In our shock tube experiments, CH radicals, produced from the pyrolysis of di- tert-butylperoxide, and H atoms, produced from the pyrolysis of CHI, were reacted with dilute mixtures of isobutane in argon at 870-1130 K and 140-360 kPa, usually with a radical chain inhibitor. Propene and isobutene, measured with GC/FID and MS, were quantified as characteristic of H-abstraction from the primary and tertiary carbons, respectively.

β-Bond Scission and the Yields of H and CH in the Decomposition of Isobutyl Radicals.

The relative rates of C-C and C-H β-scission reactions of isobutyl radicals (2-methylprop-1-yl, CH) were investigated with shock tube experiments at temperatures of (950 to 1250) K and pressures of (200 to 400) kPa. We produced isobutyl radicals from the decomposition of dilute mixtures of isopentylbenzene and observed the stable decomposition products, propene and isobutene. These alkenes are characteristic of C-C and C-H bond scission, respectively.

Gas-Phase Reactions of Isoprene and Its Major Oxidation Products.

Isoprene carries approximately half of the flux of non-methane volatile organic carbon emitted to the atmosphere by the biosphere. Accurate representation of its oxidation rate and products is essential for quantifying its influence on the abundance of the hydroxyl radical (OH), nitrogen oxide free radicals (NO ), ozone (O), and, via the formation of highly oxygenated compounds, aerosol. We present a review of recent laboratory and theoretical studies of the oxidation pathways of isoprene initiated by addition of OH, O, the nitrate radical (NO), and the chlorine atom.

Cavity ringdown spectroscopy of the hydroxy-methyl-peroxy radical.

We report vibrational and electronic spectra of the hydroxy-methyl-peroxy radical (HOCH2OO(•) or HMP), which was formed as the primary product of the reaction of the hydroperoxy radical, HO2(•), and formaldehyde, HCHO. The ν1 vibrational (OH stretch) spectrum and the à ← X̃ electronic spectrum of HMP were detected by infrared cavity ringdown spectroscopy (IR-CRDS), and assignments were verified with density functional calculations. The HMP radical was generated in reactions of HCHO with HO2(•).

Kinetics of n-butoxy and 2-pentoxy isomerization and detection of primary products by infrared cavity ringdown spectroscopy.

The primary products of n-butoxy and 2-pentoxy isomerization in the presence and absence of O(2) have been detected using pulsed laser photolysis-cavity ringdown spectroscopy (PLP-CRDS). Alkoxy radicals n-butoxy and 2-pentoxy were generated by photolysis of alkyl nitrite precursors (n-butyl nitrite or 2-pentyl nitrite, respectively), and the isomerization products with and without O(2) were detected by infrared cavity ringdown spectroscopy 20 μs after the photolysis. We report the mid-IR OH stretch (ν(1)) absorption spectra for δ-HO-1-C(4)H(8)•, δ-HO-1-C(4)H(8)OO•, δ-HO-1-C(5)H(10)•, and δ-HO-1-C(5)H(10)OO•.

Gas phase hydrogen/deuterium exchange of arginine and arginine dipeptides complexed with alkali metals.

The hydrogen/deuterium (H/D) exchange of protonated and alkali-metal cationized Arg-Gly and Gly-Arg peptides with D(2)O in the gas phase was studied using electrospray ionization quadropole ion trap mass spectrometry. The Arg-Gly and Gly-Arg alkali metal complexes exchange significantly more hydrogens than protonated Arg-Gly and Gly-Arg. We propose a mechanism where the peptide shifts between a zwitterionic salt bridge and nonzwitterionic charge solvated conformations.