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. From this review, a recommendation for a nearly complete gas-phase oxidation mechanism of isoprene and its major products is developed. The mechanism is compiled with the aims of providing an accurate representation of the flow of carbon while allowing quantification of the impact of isoprene emissions on HO and NO free radical concentrations and of the yields of products known to be involved in condensed-phase processes. Finally, a simplified (reduced) mechanism is developed for use in chemical transport models that retains the essential chemistry required to accurately simulate isoprene oxidation under conditions where it occurs in the atmosphere-above forested regions remote from large NO emissions.

Redox chemistry during the activation of carbon dioxide involves changing the charge state in a CO molecular unit. However, such changes are usually not well described by integer formal charges, and one can think of COO functional units as being in intermediate oxidation states. In this article, we discuss the properties of CO and CO-based functional units in various charge states. Besides covering isolated CO and its ions, we describe the CO-based ionic species formate, oxalate, and carbonate. Finally, we provide an overview of CO-based functional groups and ligands in clusters and metal-organic complexes.

Supporting Information 1 Characterization of Instrument Effects using NO2 PhotolysisExperiments measuring the instrument response function (IRF) used a certified mix of NO2 in He (Matheson Tri-Gas, 1.00% NO2 with 0.5% O2 as a stabilizing agent in He). We conducted NO2 photolysis experiments at 8 Torr and 10.0 eV photon energy. The NO + and NO2 + signals are shown in Figure S1. Following photolysis at t = 0, we observed a small depletion in the NO2 + and a fast rise in the NO + signal. The measured depletion of NO2 (from both photolytic and kinetic reactions) was 4.6 ± 0.5% determined by fitting the data over the time range from −20 to 20 ms. At later 1

We explore the structures of [Ti(CO) ] cluster anions using infrared photodissociation spectroscopy and quantum chemistry calculations. The existence of spectral signatures of metal carbonyl CO stretching modes shows that insertion of titanium atoms into C-O bonds represents an important reaction during the formation of these clusters. In addition to carbonyl groups, the infrared spectra show that the titanium center is coordinated to oxalato, carbonato, and oxo ligands, which form along with the metal carbonyls. The presence of a metal oxalato ligand promotes C-O bond insertion in these systems. These results highlight the affinity of titanium for C-O bond insertion processes.

The absolute photoionization spectrum of the hydroxyl (OH) radical from 12.513 to 14.213 eV was measured by multiplexed photoionization mass spectrometry with time-resolved radical kinetics. Tunable vacuum ultraviolet (VUV) synchrotron radiation was generated at the Advanced Light Source. OH radicals were generated from the reaction of O(D) + HO in a flow reactor in He at 8 Torr. The initial O(D) concentration, where the atom was formed by pulsed laser photolysis of ozone, was determined from the measured depletion of a known concentration of ozone. Concentrations of OH and O(P) were obtained by fitting observed time traces with a kinetics model constructed with literature rate coefficients. The absolute cross section of OH was determined to be σ(13.436 eV) = 3.2 ± 1.0 Mb and σ(14.193 eV) = 4.7 ± 1.6 Mb relative to the known cross section for O(P) at 14.193 eV. The absolute photoionization spectrum was obtained by recording a spectrum at a resolution of 8 meV (50 meV steps) and scaling to the single-energy cross sections. We computed the absolute VUV photoionization spectrum of OH and O(P) using equation-of-motion coupled-cluster Dyson orbitals and a Coulomb photoelectron wave function and found good agreement with the observed absolute photoionization spectra.

We present IR spectra and quantum chemical calculations for anionic iron-CO clusters of the form [Fe(CO)] (n = 3-7). All observed clusters have at least two CO units strongly bound to the metal atom. These strongly bound iron-CO complexes form the core ions of the clusters and are solvated by additional, weakly bound CO molecules. Larger clusters show clear infrared signatures of core ion isomers with three CO moieties as well. Dominant structural motifs are based on bidentate CO ligands with Fe-O/Fe-C bonds, oxalate ligands, and metal insertion into a CO bond.

We study small titanium oxide-CO cluster anions in vacuo to understand the fundamental interactions between TiO and CO in the presence of an excess electron. Infrared spectra of [TiO (CO) ] ( x = 1-3, y > 1) were obtained using photodissociation spectroscopy and assigned through quantum chemistry calculations, identifying the formation of carbonato, oxalato, oxo, η-(O,O), and carbonyl ligands in the core ions of these clusters, with carbonato ligands being the dominant ligand species.

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