ACS Earth and Space Chemistry最新文献

Glycine and its methyl ester hydrochloride were investigated in superacidic media HF/MF₅ (M = As, Sb). The diprotonated species were obtained as [MF₆]⁻ salts (M = As, Sb). The colorless salts were characterized by vibrational spectroscopy, NMR spectroscopy, and single-crystal diffraction. Glycinoyl fluoride was isolated for the first time as a solid and characterized by vibrational spectroscopy, NMR spectroscopy, and single X-ray diffraction. Glycinoyl fluoride was investigated in the superacidic medium HF/MF₅ (M = As, Sb). The salts of the diprotonated species were obtained and characterized by vibrational spectroscopy. The experimental data are discussed together with quantum chemical calculations at the M06-2X/aug-cc-pVTZ level of theory.

A heterogeneous dust chemistry module was developed and coupled toward the near-explicit mechanism MCM. Model simulations were performed for different dust concentrations (low, high, and very high dust), and the most significant changes were modeled in HNO₃, by 99% for very high dust, forming surface nitrates. Surface photolysis of nitrates resulted in an increase in HONO. Chemical rate analyses revealed that the direct uptake on dust played only a minor role for most species, except N₂O₅, HNO₃, H₂O₂, and SO₂. Average SO₂ oxidation rates of 3 μg m^–3 h^–1 and 0.3 μg m^–3 h^–1 were modeled for dust loads of 196 μg m^–3 and 19.6 μg m^–3, which are higher than the reported aqueous-phase oxidation rates. Sensitivity simulations considering the uptake of only one compound revealed that the N₂O₅ and HNO₃ uptake had the strongest effects. The uptake of only HNO₃ with surface photolysis resulted in major increases in NO_x, OH, and HONO by 20%, 36%, and 5110%, respectively. Further sensitivity simulations with higher uptake coefficients showed that the uptake of O₃ could act as an indirect source of HONO because of higher NO_x and OH concentrations. The minimum required uptake coefficient for direct effects to occur (γ_min) was also determined for the main inorganic species and had values of 10^–6 for O₃ and SO₂ and 10^–4 for NO₂, thus suggesting that direct uptake of NO₂ on dust is an unimportant sink under urban conditions. Overall, this study shows the importance of photoenhanced uptake and uptake coefficient values in heterogeneous chemistry.

The exploration of iron-containing species represents a prominent area in contemporary astrochemical investigations. Iron in the interstellar medium exhibits predominantly low concentrations, hinting at the potential presence of missing iron in either a condensed or molecular state. The FeC₄H₂ neutral system has been investigated using computational calculations, emphasizing the hypothesis that missing iron may exist as iron–carbon hydride compounds or their higher order. A total of 61, 46, and 36 stationary points have been identified on the potential energy surface (PES) of the FeC₄H₂ in the singlet, triplet, and quintet electronic states, respectively, showcasing the existence of a planar tetracoordinate iron (ptFe). A linear geometry represents the global minimum on the PES of FeC₄H₂ as observed in the quintet ground electronic state. Meanwhile, the ptFe geometry is identified as the second most stable isomer in the quintet electronic state, which is the lowest energy solely in the singlet electronic state. Further, the observed ptFe geometry closely resembles the experimentally detected FeC₄ molecule in the gas phase. In light of its similarity to FeC₄ and the recent detection of FeC in the interstellar medium, the ptFe would be a potential astrophysical molecule that will also be identified in the gas phase. From that point of view, a comprehensive examination of the nature of chemical bonding of the ptFe geometry in the singlet, triplet, and quintet electronic states has been characterized, which dictates the stabilization of ptFe through multicenter bonding with surrounding carbon atoms. Ab initio molecular dynamics simulations revealed the dynamic stability of the system. Understanding the interstellar species with its structure and chemical bonding is an important aspect that would shed light on new insights into the experimental observations in the future.

Terebic acid (C₇H₁₀O₄) is a biogenic secondary organic aerosol constituent, produced by the oxidation of first- and second-generation products of monoterpenes such as α-pinene, β-pinene, and Δ³-carene. It is a processed derivative of terpenylic acid and has been identified in aerosol samples from terrestrial and forest environments. The physicochemical properties of pure terebic acid aerosol were characterized using two different atmospheric simulation chambers and a suite of online particle and gas-phase instrumentation. Its mass spectrum, obtained by a high-resolution time-of-flight mass spectrometer, had characteristic peaks at mass-to-charge (m/z) ratios 81, 96, 100, 115, and 143, mainly related to oxygenated fragment ions. The density of terebic acid aerosol was 1.33 ± 0.20 g cm^–3, and its vaporization enthalpy was 85 kJ mol^–1. The estimated saturation concentration at 298 K of 2.6 ± 1.2 μg m^–3 places terebic acid in the semivolatile organic compound category. Oxidation of terebic acid aerosol by hydroxyl (OH) radicals resulted in a substantial reduction in organic aerosol (OA) mass concentration (up to 80%), with no significant alteration in the OA spectrum or aerosol O:C ratio, indicating negligible production of secondary OA. Gas-phase analysis detected the production of smaller compounds, such as acetone. The terebic acid oxidation products were mostly in the gas phase as fragmentation appears to dominate its reaction with OH radicals. The gas-phase reaction rate constant with OH was estimated to be 3 × 10^–12 cm³ molecule^–1 s^–1.

Manganese (Mn)-oxides regulate carbon (C) cycling in soils by sorbing and oxidizing organic compounds. The composition of soil organic matter varies widely, and little is known about the reactivity of individual organic compounds with structurally diverse Mn-oxides under various environmentally relevant pH conditions. Here, we examined the affinity of six organic compounds for three Mn-oxides, comprised of layer (birnessite and hydrous Mn oxide HMO) or tunnel (cryptomelane) structures, at acidic (pH 4), slightly acidic (pH 6), and slightly alkaline (pH 8) conditions. Cryptomelane, with a higher specific surface area and point of zero charge, showed higher reactivity than that of HMO and birnessite. Interestingly, these Mn-oxides, although different in structures, decomposed each organic compound to form the same products. Citrate, pyruvate, ascorbate, and catechol induced reduction and dissolution of Mn-oxides. After the reaction, the average oxidation state of Mn in the solids was much lower at pH 4 than at pH 6 and 8, suggesting more reduction under more acidic conditions. Even when reacting with phthalate and propanol, which only sorbed to Mn-oxides but did not degrade, there was proton-promoted Mn dissolution under acidic conditions. These results suggest the significance of environmental pH and mineral structures in affecting the Mn–organic interactions and provide fundamental insights into a better understanding of the roles of Mn-oxides in regulating soil C cycling.

Soil mineralogy plays a vital role in carbon storage. Birnessite is a widely occurring manganese oxide mineral. Despite its widespread occurrence, studies of the interactions between natural soil organic carbon and manganese oxide minerals are rare. This study investigated the influence of triclinic birnessite on the transformation of vermicompost-derived dissolved organic carbon (DOC) at different pHs (4 and 8) and temperatures (25 and 50 °C). Enhanced adsorption and transformation of DOC, particularly at pH 4 and 50 °C, were observed. The use of SUVA₂₅₄ and fluorescence spectroscopy showed that DOC sorption caused an increase in carbon aromaticity, with the highest degree observed at pH 4 at 50 °C. In particular, X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure C 1s characterization showed an 8-fold increase in aromaticity at 50 °C compared to the unreacted DOC, with esterification and/or etherification reactions also occurring at pH 4. The impact of DOC sorption on birnessite stability and transformations was also assessed via X-ray absorption near-edge structure spectroscopy, which revealed that reacted and unreacted triclinic birnessite showed modest changes to Mn II, III, and IV. Manganese K-edge extended X-ray absorption fine structure spectroscopy showed the increased formation of hexagonal birnessite at pH 4, the formation of manganite at pH 4 and 8, 50 °C, and the formation of up to 6% ramsdellite at pH 8, 25 °C. This study provides new insights into the role of birnessite in soil carbon storage and manganese mineral transformations under environmentally relevant conditions.

Light and condensate oils are high-quality fossil energy sources. Because light and condensate oils have complex origins and are generally dominated by light hydrocarbons with few diagnostic biomarkers, conventional geochemical methods have difficulty identifying their categories, especially in complex petroleum systems. In this study, the fluorescence lifetime (τ_oil) and fluorescence spectral parameters (λ_max, Q_510/430, and Q_650/500) of light and condensate oils in the northern Tazhong Uplift of the Tarim Basin were systematically analyzed. The results indicate that the light and condensate oils in this area can be divided into three categories according to their fluorescence characteristics. For the TZ-I, TZ-II, and TZ-III oils, τ_oil progressively increases, and the fluorescence spectra gradually shift blue with decreases in Q_510/430, Q_650/500, and λ_max, which results from the successive decreases in gas invasion extent for the three types of Tazhong oils. Light hydrocarbons mainly consisting of saturated hydrocarbon fractions were carried by highly mature gaseous hydrocarbons from deep sources to relatively shallow reservoirs and mixed with early accumulated crude oils. The charged saturates reduced the fluorophore (polycyclic aromatic hydrocarbons, PHA) concentration in crude oil, weakened fluorescence quenching, and promoted fluorescence emission, which changed the fluorescence characteristics of crude oils. Correlation diagrams based on different fluorescence parameters as well as other parameters, including physical, geochemical, and associated gas parameters, provide a favorable method for determining light and condensate categories. Moreover, the fluorescence method exhibits great application potential for direct correlations between reservoir oils and inclusion oils in complex petroleum systems.