Photochemical and thermochemical pathways to S and polysulfur formation in the atmosphere of Venus.

Polysulfur species have been proposed to be the unknown near-UV absorber in the atmosphere of Venus. Recent work argues that photolysis of one of the (SO) isomers, cis-OSSO, directly yields S with a branching ratio of about 10%. If correct, this pathway dominates polysulfur formation by several orders of magnitude, and by addition reactions yields significant quantities of S, S, and S.

Oxygen isotopic heterogeneity in the early Solar System inherited from the protosolar molecular cloud.

The Sun is O-enriched (ΔO = -28.4 ± 3.6‰) relative to the terrestrial planets, asteroids, and chondrules (-7‰ < ΔO < 3‰).

A light carbon isotope composition for the Sun.

Measurements by the Genesis mission have shown that solar wind oxygen is depleted in the rare isotopes, O and O, by approximately 80 and 100‰, respectively, relative to Earth's oceans, with inferred photospheric values of about -60‰ for both isotopes. Direct astronomical measurements of CO absorption lines in the solar photosphere have previously yielded a wide range of O isotope ratios. Here, we reanalyze the line strengths for high-temperature rovibrational transitions in photospheric CO from ATMOS FTS data, and obtain an O depletion of δO = -50 ± 11‰ (1σ).

Early inner solar system origin for anomalous sulfur isotopes in differentiated protoplanets.

Achondrite meteorites have anomalous enrichments in (33)S, relative to chondrites, which have been attributed to photochemistry in the solar nebula. However, the putative photochemical reactions remain elusive, and predicted accompanying (33)S depletions have not previously been found, which could indicate an erroneous assumption regarding the origins of the (33)S anomalies, or of the bulk solar system S-isotope composition. Here, we report well-resolved anomalous (33)S depletions in IIIF iron meteorites (<-0.

Oxygen isotope anomaly observed in water vapor from Alert, Canada and the implication for the stratosphere.

To identify the possible anomalous oxygen isotope signature in stratospheric water predicted by model studies, 25 water vapor samples were collected in 2003-2005 at Alert station, Canada (82°30'N), where there is downward transport of stratospheric air to the polar troposphere, and were analyzed for δ(17)O and δ(18)O relative to Chicago local precipitation (CLP). The latter was chosen as a reference because the relatively large evaporative moisture source should erase any possible oxygen isotope anomaly from the stratosphere. A mass-dependent fractionation coefficient for meteoric waters, λMDF(H2O) = 0.

High-resolution study of 13C16O A-X(v' = 0-9) bands using the VUV-FTS at SOLEIL: revised term values.

We present high-resolution absorption spectral measurements of the A(1)Π-X(1)Σ(+) band system of (13)C(16)O. These were recorded with the VUV Fourier transform spectrometer (VUV-FTS) installed on the DESIRS beamline at the SOLEIL synchrotron. This work includes revised term values that extend to higher J' values than previous measurements for most v' levels and lower J' values for v' = 0.

Unique Hg stable isotope signatures of compact fluorescent lamp-sourced Hg.

The recent widespread adoption of compact fluorescent lamps (CFL) has increased their importance as a source of environmental Hg. Stable isotope analysis can identify the sources of environmental Hg, but the isotopic composition of Hg from CFL is not yet known. Results from analyses of CFL with a range of hours of use show that the Hg they contain is isotopically fractionated in a unique pattern during normal CFL operation.

The kinetics study of the S + S2 → S3 reaction by the chaperone mechanism.

The recombination of S atoms has been found to be stepwise from the smallest unit, the elemental S atom, to the most abundant molecule S(8). The reaction between S + S(2) → S(3) has not been reported either experimentally or by theory, but may be a key intermediate step in the formation of sulfur aerosols in low-O(2) atmospheres. In this work, the kinetics of this reaction is reported with Ar gas used as the chaperone molecule in the production of S(3) via two complex intermediates: SAr + S(2) and S(2)Ar + S.

Comment on "Experimental test of self-shielding in vacuum ultraviolet photodissociation of CO".

Chakraborty et al. (Reports, 5 September 2008, p. 1328) demonstrated very large, wavelength-dependent mass-independent isotopic effects during carbon monoxide (CO) photodissociation and argued that self-shielding in CO was not responsible.

Identification of the reactive cis,mer isomer of [Ir(CO)2I3Me]-: relation to the mechanism of iridium-catalyzed methanol carbonylation.

Thermal dissociation of CO from cis,fac-[Ir(CO)(2)I(3)Me](-) (1a) gives the iodide-bridged dimer [{Ir(CO)I(2)(mu-I)Me}(2)](2-), which was characterized crystallographically as its Ph(4)As(+) salt. This dimer reacts with CO at ambient temperature to give the acetyl complex trans,mer-[Ir(CO)(2)I(3)(COMe)](-). An intermediate in this reaction is the previously unobserved cis,mer-[Ir(CO)(2)I(3)Me](-) (1b), which was characterized by IR and NMR spectroscopy.

An ab initio study of the low-lying electronic states of S3.

Accurate calculations of the low-lying singlet and triplet electronic states of thiozone, S(3), have been carried out using large multireference configuration interaction wave functions. Cuts of the full potential energy surfaces along the stretching and bending coordinates have been presented, together with the vertical excitation spectra. The strong experimentally observed absorption around 395 nm is assigned to the 1 (1)B(2) state, which correlates to ground state products.

High-level ab initio studies of the structure, vibrational spectra, and energetics of S3.

Observation of mass-dependent and non-mass-dependent sulfur isotope fractionations in elemental sulfur is providing new insight into the nature of the sulfur cycle in the atmosphere. Interpretation of the experimental isotope data requires estimation of the energetics for the reaction S+S2-->S3 (isoelectronic with O+O2-->O3). Key molecular properties of the S3 potential-energy surface, such as vibrational frequencies and isotopic shifts, are presented that can be used to assess the mass-dependent fractionation effect.