Efficient low-temperature oxidation of carbon-cluster anions by SO2

Carbon-cluster anions, CN-, are very reactive toward SO2 (sticking probability of 0.012 +/- 0.005 for C27- at 25 degrees C), in contrast to their inertness toward other common atmospheric gases and pollutants. In flow reactor experiments at ambient temperature and near atmospheric pressure, primary adsorption of SO2 by the carbon cluster anions, N = 4-60, yields CNSO2- or CN-1S-. The inferred elimination of neutral CO2 is also detected as meta-stable decay in collision-induced dissociation. At higher temperatures, the reaction of SO2 with nascent carbon clusters yields CN-1SO- as well as undetected CO. The size-dependent initial reactivity reflects the previously established structural transitions (i.e., from chain to cyclic to cage structures). Such carbon clusters are formed in sooting flames and may act as nuclei for the formation of primary soot particles and serve as models for the local structural features of active soot particle sites for black-carbon soot. The facile generation of reactive carbon-sulfide and -sulfinate units may therefore have implications for understanding the health and environmental effects attributed to the coincidence of soot and SO2.     

IRMPD spectroscopy of anionic group II metal nitrate cluster ions

Anionic group II metal nitrate clusters of the formula [M₂(NO₃)₅]⁻, where M₂ = Mg₂, MgCa, Ca₂, and Sr₂, are investigated by infrared multiple photon dissociation (IRMPD) spectroscopy to obtain vibrational spectra in the mid-IR region. The IR spectra are dominated by the symmetric and the antisymmetric nitrate stretches, with the latter split into high and low-frequency components due to the distortion of nitrate anion symmetry by interactions with the cation. Density functional theory (DFT) is used to predict geometries and vibrational spectra for comparison to the experimental spectra. Calculations yield two stable isomers: the first one contains two terminal nitrate anions on each cation and a single bridging nitrate (“mono-bridging”), while the second structure features a single terminal nitrate on each cation with three bridging nitrate ligands (“tri-bridging”). The tri-bridging isomer is calculated to be lower in energy than the mono-bridging one for all species. Theoretical spectra of the tri-bridging structure provide a better qualitative match to the experimental infrared spectra of [Mg₂(NO₃)₅]⁻ and [MgCa(NO₃)₅]⁻. However, the profile of the low-frequency ν ₃ band for the Mg₂ complex suggests a third possible isomer not predicted by theory. The IRMPD spectra of the Ca₂ and Sr₂ complexes are better reconciled by a weighted summation of the spectra of both isomers suggesting that a mixture of structures is present.     

Infrared spectrum of potassium‐cationized triethylphosphate generated using tandem mass spectrometry and infrared multiple photon dissociation

Tandem mass spectrometry and wavelength‐selective infrared photodissociation were used to generate an infrared spectrum of gas‐phase triethylphosphate cationized by attachment of K⁺. Prominent absorptions were observed in the region of 900 to 1300 cm^?1 that are characteristic of phosphate P?O and P? O? R stretches. The relative positions and intensities of the IR absorptions were reproduced well by density functional theory (DFT) calculations performed using the B3LYP functional and the 6‐31+G(d), 6‐311+G(d,p) and 6‐311++G(3df,2pd) basis sets. Because of good correspondence between experiment and theory for the cation, DFT was then used to generate a theoretical spectrum for neutral triethylphosphate, which in turn accurately reproduces the IR spectrum of the neat liquid when solvent effects are included in the calculations. Copyright © 2009 John Wiley & Sons, Ltd.