Reaction of (μ-H)₂Os₃(CO)₉(PPh₃) with Acetylene and Ethylene. Structures, Dynamics, and Interconversion of Two Isomers of the Vinyl Complex (μ-H)Os₃(CO)₉(PPh₃)(μ-CHCH₂)

As reported previously by Brown and Evans, the reaction of (μ-H)2Os3(CO)9(PPh3) with acetylene provides two isomers of the hydrido vinyl compound (μ-H)Os3(CO)9(PPh3)(μ-η2-CHCH2) (2). The solid-state structures of these two isomers now have been defined by single-crystal X-ray crystallography. The major isomer 2a contains a triangular array of osmium atoms with the vinyl ligand bridging the Os(2)−Os(3) edge, forming a σ-bond to Os(3) and a π-bond to Os(2), and the triphenylphosphine ligand coordinating to Os(2) in an “in-plane” position. The presence of the hydride ligand also bridging the Os(2)−Os(3) edge was deduced indirectly. The minor isomer 2b also contains a triangular Os3 array with the vinyl ligand bridging the Os(2)−Os(3) edge and forming a σ-bond to Os(2) and a π-bond to Os(3). The triphenylphosphine ligand is bound to Os(1). The presence of the bridging hydride on the Os(1)−Os(3) edge was not directly detected but was supported by analysis of the structure; the hydride ligand therefore does not bridge the same edge as the vinyl moiety. The solution structures and dynamics of 2a and 2b have been investigated by variable-temperature 13C NMR and 13C spin saturation transfer experiments; isomer 2a exhibits evidence for nondegenerate σ/π bond interchange in the bridging vinyl group. Separation of 2a and 2b can be effected by thin-layer chromatography (silica; CH2Cl2/C6H14, 1:3); subsequent 1H NMR spectra reveal slow equilibration of 2a and 2b (t1/2 = 85 min, 2a:2b = 2.2:1 at equilibrium). The same mixture of isomers is formed from the reaction of 1 with ethylene at high pressure (500 psig), with the previously characterized complex (μ-H)2Os3(CO)9(PPh3)(μ-CHCH3) as an intermediate

Improved technique for measuring the size distribution of black carbon particles in liquid water

<p>We developed an improved technique for measuring the size distribution of black carbon (BC) particles suspended in liquid water to facilitate quantitative studies of the wet deposition of BC. The measurement system, which consists of a nebulizer and a single-particle soot photometer, incorporates two improvements into the system that we developed earlier. First, we extended the upper limit of the detectable BC size from 0.9 μm to about 4.0 μm by modifying the photo-detector for measuring the laser-induced incandescence signal. Second, we introduced a pneumatic nebulizer (Marin-5) with a high extraction efficiency (∼50.0%) that was independent of particle diameter up to 2.0 μm. For BC mass concentrations less than 70 μg L⁻¹, we experimentally showed that the diameters of BC particles did not appreciably change during the Marin-5 extraction process, consistent with theoretical calculations. Finally, we demonstrated by laboratory experiments that the size distributions of ambient BC particles changed little during their growth into cloud droplets under supersaturation of water vapor. Using our improved system, we measured the size distributions of BC particles simultaneously in air and rainwater in Tokyo during summer 2014. We observed that the size distributions of BC particles in rainwater shifted to larger sizes compared with those observed in ambient air, indicating that larger BC particles in air were removed more efficiently by precipitation.</p> <p>Copyright © 2016 American Association for Aerosol Research</p

Mass absorption cross section of black carbon for Aethalometer in the Arctic

Long-term measurements of the mass concentration of black carbon (BC) in the atmosphere (MBC) with well-constrained accuracy are indispensable to quantify its emission, transport, and deposition. The aerosol light absorption coefficient (babs), usually measured by a filter-based absorption photometer, including an Aethalometer (AE), is often used to estimate MBC. The measured babs is converted to MBC by assuming a value for the mass absorption cross section (MAC). Previously, we derived the MAC for AE (MAC (AE)) from measured babs and independently measured MBC values at two sites in the Arctic. MBC was measured with a filter-based absorption photometer with a heated inlet (COSMOS). The accuracy of the COSMOS-derived MBC (MBC (COSMOS)) was within about 15%. Here, we obtained additional MAC (AE) measurements to improve understanding of its variability and uncertainty. We measured babs (AE) and MBC (COSMOS) at Alert (2018–2020), Barrow (2012–2022), Ny-Ålesund (2012–2019), and Pallas (2019–2022). At Pallas, we also obtained four-wavelength photoacoustic aerosol absorption spectrometer (PAAS-4λ) measurements of babs. babs (AE) and MBC (COSMOS) were tightly correlated; the average MAC (AE) at the four sites was 11.4 ± 1.2 m2 g−1 (mean ± 1σ) at 590 nm and 7.76 ± 0.73 m2 g−1 at 880 nm. The spatial variability of MAC (AE) was about 11% (1σ), and its year-to-year variability was about 18%. We compared MAC (AE) in the Arctic with values at mid-latitudes, measured by previous studies, and with values obtained by using other types of filter-based absorption photometer, and PAAS-4λ. Copyright © 2024 American Association for Aerosol Research</p