ACS Earth and Space Chemistry最新文献

Reactive organic carbon (ROC) from volatile chemical products (VCPs) has emerged as an important precursor to urban ozone and secondary organic aerosol (SOA). Oxygenated ROC from VCPs may contribute to unexplained urban SOA; however, a predictive understanding is hampered by the structural complexity of multifunctional oxygenates. These functional groups may alter oxidation rates and open reaction pathways that are unavailable to hydrocarbons. We examine the OH-initiated oxidation of 2-(2-ethoxyethoxy)ethanol (2-2-EEE, C₆H₁₄O₃), a potential contributor to urban SOA and a model compound for glycol diethers, which are commonly used as industrial solvents in paints, resins, and enamels. Our gas and particle-phase observations approach carbon closure (65(±14)%–107(±39)% of initial 2-2-EEE carbon accounted for at 15 h photochemical age) with stable reaction products that can be explained by a combination of peroxy radical (RO₂) H-shifts, RO₂ + HO₂, and RO₂ + NO reactions. Carbon-retaining (C₆) products are consistent with hydroperoxy carbonyl species, including esters, and likely arise from a combination of RO₂ H-shifts that are promoted by the diether structure, and RO₂ + HO₂ reactions. These products contribute to SOA and result in mass yields of 0.04–0.14. Rate coefficients from structure–activity relationships demonstrate that the diether structure drives rapid alkoxy radical (RO) decomposition and exerts important control over 2-2-EEE aerosol formation when RO₂ + NO reactions are competitive. Functionalized C₅-products dominate gas-phase carbon and likely arise from at least one RO₂ H-shift, followed by RO decomposition. Our results highlight the importance of multiple oxygen-containing functional groups in controlling the reactive fate of 2-2-EEE, with relevance to other oxygenated VCP ROC emissions.

The Dragonfly mission is set to explore Titan’s surface in the mid-2030s. This relocatable lander is equipped with the Dragonfly Mass Spectrometer (DraMS) instrument. One of DraMS functioning mode is gas chromatography–mass spectrometry, to identify organic compounds in solid samples. DraMS-GC includes two independent chemical injection traps to focus the molecules released from the sample. Initially, Tenax TA was planned to be the adsorbent in the injection traps because of its heritage in previous space probes. However, Tenax TA has shown some decomposition products that challenge the identification of the molecules indigenous to the sample. In this work, the performance of another adsorbent powder, Carbotrap C, was compared to Tenax TA. Performance was evaluated in DraMS-like desorption conditions by comparing the recovery yield after adsorption and desorption of a set of 53 organic compounds of interest to Titan. Recovery with Carbotrap C was either similar or better than with Tenax TA for 79% of compounds. This recovery yield was further improved by increasing the desorption temperature. DraMS low desorption flow rate appears to be the most limiting parameter for recovery. Desorption from both Tenax TA and Carbotrap C led to partial but comparable racemization for three of the four amino acids that were enantiomerically resolved. Together, these results led to the integration of Carbotrap C in one of the DraMS injection traps.

The third member of the Laiyang Formation (K₁l₃) within the Sulu orogenic belt has been continuously depositing fine-grained sediments. However, the depositional characteristics and formation mechanisms of this Late Mesozoic fine-grained rock series remain poorly understood. In this study, the integration of sedimentology with petrology and geochemistry of fine-grained rocks belonging to K₁l₃ in the southern Riqingwei Basin allows us to analyze the macro- and microsedimentary structures, paleoenvironmental evolution, and dynamic sedimentary processes. The evidence indicates that gravity flow was the key mechanism for the long-distance transport of fine-grained materials in K₁l₃, along the gentle slope in deep-water settings. The fine-grained mud-rich sedimentary system in this area consists of laminated and massive siliciclastic fine-grained rocks. The TOC content is generally low (0.46–2.20%, avg. 0.97%), and most samples are “organic-bearing” fine-grained sedimentary rocks. Amorphous organic matter is the dominant maceral component, followed by opaque phytoclasts and collinite. By utilizing CIA and C-value to assess paleoclimate, Ti content, Al content, K/Al, and Rb/Al to characterize detrital flux, Sr/Ba to interpret paleosalinity, V/(V + Ni), V_EF, and U_EF to analyze redox conditions, and Cu_EF, Zn_EF, and Ni_EF to evaluate paleoproductivity, the depositional environment of the K₁l₃ fine-grained rocks was reconstructed. The climate during this period was relatively arid with limited terrestrial input. Moreover, the seawater was anoxic, and the productivity was at a low to moderate level. The vertical variations in the geochemical profile of Well LK-1 indicate that the primary productivity and redox conditions significantly influenced the organic matter enrichment in the fine-grained sediments. Turbidity currents are important processes for the transport of clasts and terrestrial organic matter to the distal region of the deep-water setting. Based on the aforementioned interpretations, the depositional model of K₁l₃ in the southern Riqingwei Basin was established, providing new insights into the origin of deep-water fine-grained rocks.

Molecular dynamics (MD) calculations were carried out to simulate the solar wind irradiation, namely, H⁺, of methane–ammonia ices. To mimic a continuous ion bombardment of the ice, multiple impact cycles were performed on the ice target. Each impact cycle involved seven 0.829 keV H⁺ (total energy of 5.8 keV and a velocity of 400 km/s) impacting the surface for a duration of 0.5 ps, which was shown in previous work to be a sufficient time for any product resulting from H⁺ impacts of the ice to form and stabilize. At the end of each cycle, the ice was quenched to 15 K to prevent excessive heating and sublimation. The dominant radiolysis species formed in our simulations were those obtained from the reaction of methyl and amino radicals, namely, ethane, hydrazine, and methylamine. The formation of methylamine, the building block of the amino acid glycine, is in agreement with observations and previous irradiation experiments. Additional species resulting from progressive impact-mediated hydrogen loss of simple two-radical products, namely, ethyl, methanimine, aminomethyl, and diimine, were produced in significant quantities in our simulations and in previous irradiation experiments. Unsaturated molecules, such as vinyl, ethylene, and acetylene, were formed to a lesser extent by impact-mediated hydrogen loss. Larger product species, such as methanediamine, requiring the reaction of up to four radicalized ice molecules did form throughout the course of our simulations and were also obtained in previous irradiation experiments. Methanediamine is a precursor to nucleobases.

A computational protocol based on the minimum energy principle has been applied to the C₃H₆O₂ isomer family, providing accurate energetic hierarchies and spectroscopic parameters relevant to astrochemistry. The calculations predict propanoic acid as the most stable isomer, followed by methyl acetate, ethyl formate, 1-hydroxyacetone, 2- and 3-hydroxypropanal. The protocol delivers computed rotational spectroscopic parameters, and their accuracy has been benchmarked against literature results for seven C₃H₆O₂ isomers and further validated through new high-frequency measurements of glycidol, c-C₂H₃O-CH₂OH. Its rotational spectrum has been recorded in the 65–120, 146–330, and 440–520 GHz ranges, extending the frequency coverage with respect to previous studies. The improved set of spectroscopic parameters for glycidol provides a basis for future radioastronomical searches in the interstellar medium. Furthermore, the benchmarking strategy establishes reliable uncertainties for the species not yet characterized in the laboratory.

In this theoretical study, the possibility of forming important prebiotic molecules such as hydrogen cyanide, acetylene, and nitrogen-containing heterocyclic compounds in Titan’s atmosphere via the sequential reactions of methylidyne radicals, denoted as ²CH, with N₂ molecules is explored. The state-of-the-art quantum-chemical methods such as CCSD(T)-F12 and CCSDT(Q) are employed to calculate reliable molecular electronic energies. Next, the rate coefficients for the formation of products are computed by a transition-state and RRKM statistical rate theory. A master equation analysis is employed to calculate deactivation of energized intermediates. A special version of a RRKM theory, VRC-TST, is used for computing unimolecular dissociation of bond scission processes. It is found that first, the CH radical reacts with the N₂ molecule to form the HCNN radical. The calculations reveal that HCNN is produced efficiently at pressures and temperatures corresponding to the atmosphere of Titan. Next, an HCNN radical could undergo self reaction or react with an additional CH radical. According to the present study, both latter reactions are fast barrierless processes and lead to hydrogen cyanide and acetylene molecules.

The kinetics and products of the reaction of OH radicals with ethylene were studied using a low-pressure discharge-flow reactor combined with modulated molecular beam mass spectrometry. The total rate constant of the reaction (k₁) was determined as a function of pressure (0.4–20 Torr of helium) and temperature (240–1000 K). The title reaction was found to proceed through two channels: adduct forming and H atom abstraction. For the addition channel, the high- and low-pressure limit rate coefficient were extracted from a global fit of the fall off curves observed at different temperatures (present low pressure and available in the literature high-pressure data for the reaction rate constant) with the two-parameter expression $k=\frac{k_0{k}_{\infty }\left[M\right]}{k_0\left[M\right]+k_{\infty }}\times {0.6}^{{(1+{\left(\log \left(\frac{k_0\left[M\right]}{k_{\infty }}\right)\right)}^2)}^{-1}}$: k₀ = 4.6 × 10^–29 (T/298)^−3.9 cm⁶ molecule^–2 s^–1, k_∞ = 8.0 × 10^–12 (T/298)^−1.0 cm³ molecule^–1 s^–1 in the temperature range 240–470 K. Moreover, this parametrization was found to reasonably reproduce existing measurements of k₁ with N₂ bath gas down to 69 K. The hydrogen atom abstraction channel was found to be the only important reaction pathway at T > 700 K. The rate constant of this reaction channel was determined in the temperature range 375–1000 K, as being equal to the overall rate constant at T > 700 K, and through the measurements of the yield of the reaction product, C₂H₃ radical, at T = 375–690 K: k_1b = (1.43 ± 0.10) × 10^–14 (T/298)^{3.96 ± 0.09} cm³ molecule^–1 s^–1. This expression was found to describe well earlier shock tube measurements at high temperatures (up to 1930 K) and can be recommended for use in the temperature range 375–1930 K. The rate constants measured in this study for both addition and abstraction channels are in good agreement with available theoretical calculations.

Organosulfates (OS) are emerging as a prominent secondary organic aerosol component, which can significantly alter the physicochemical properties and thus broader impacts of atmospheric aerosols. Despite their importance, OS-containing mixtures have yet to be studied using a detailed thermodynamic model which can account for the nonideal mixing among all species. In this work, we have extended the Aerosol Inorganic–Organic Mixtures Functional groups Activity Coefficients (AIOMFAC) model, a robust thermodynamic model that predicts activity coefficients in aerosol mixtures, to support OS-containing mixtures, including solving for the partial dissociation of OS. Simultaneously, we have extended AIOMFAC to support the partial dissociation of dicarboxylic acids (DA). DA are a prevalent class of compounds in tropospheric aerosols, whose pH-dependent dissociation can significantly impact aerosol physicochemical properties. We show that, for simple OS-containing and DA-containing systems, AIOMFAC is able to predict water activity and acidity (pH) behaviors that are physically reasonable and agree well with measurements, including new water activity and pH measurements performed for this study. To date, partial dissociation support in AIOMFAC is limited to select OS (methyl sulfate, ethyl sulfate, isoprene-OS-3, and isoprene-OS-4) and select DA (malonic acid, succinic acid, and glutaric acid) in simple single-phase mixtures. However, as more thermodynamic data become available, AIOMFAC’s treatment of organic acids can be further refined and expanded, enabling it to predict how the partial dissociation of organic acids affects the physicochemical properties of realistic multicomponent, multiphase aerosol systems.

Low-energy cosmic rays (E ≲ 1 GeV) are responsible for the ionization and heating of molecular clouds. While the role of supra-thermal electrons produced in the ionization process in inducing excitation of the ambient gas (mostly molecular hydrogen) has been studied in detail, the role of primary cosmic-ray nuclei (protons and heavier nuclei) has been generally neglected. Here, we introduce, for the first time, cross sections for proton impact on H₂, calculated using the semiclassical implementation of the molecular convergent close-coupling method. Our findings show that proton-induced H₂ excitation is comparable in magnitude to that caused by electrons. We discuss the possible implications on the estimate of the cosmic-ray ionization rate from observations in the near-infrared domain and on the cosmic-ray-induced H₂ ultraviolet luminescence. We also derive a new approximated analytical parametrization of the spectrum of secondary electrons that can be easily incorporated in numerical codes.