ACS Earth and Space Chemistry最新文献

The atmospheric and astrochemicaloxidation chemistryof iminesremains poorly understood despite their importance as intermediatesin nitrogen-containing organic and prebiotic chemistry. In this work,we report the first comprehensive conformer-specific theoretical investigationof the OH-initiated oxidation of N-methylethanimine(CH₃CH═NCH₃) under both terrestrial atmosphericand interstellar medium (ISM) conditions. Ab initio/DFT calculations, i.e., CCSD(T)/6-311++(3df,3pd)//ωB97X-D/6-311++(3df,3pd),combined with microcanonical variational transition state theory (μVTST)and Rice–Ramsperger–Kassel–Marcus/Master Equation(RRKM/ME) simulations reveal that the reaction proceeds through stronglystabilized prereactive complexes (PRCs), followed by competing OH-additionand H-abstraction pathways. The calculated rate coefficients werefound to be in the range of 10^–11 to 10^–12 cm³ molecule^–1 s^–1 between 200 and 400 K, consistent with analogous imine systems reportedin previous studies. The estimated atmospheric lifetime of approximately16 days suggests that CH₃CH═NCH₃ is arelatively moderate live intermediate; nevertheless, its oxidationchemistry may contribute to the formation of hazardous nitrogen-containingspecies and volatile organic compounds. The pressure-dependent kineticanalysis under ISM conditions predicts efficient low-temperature formationof acetaldehyde (CH₃CHO) and NHCH₃ radicalswith effective association rate coefficients in the range of 10^–9 to 10^–10 cm³ molecule^–1 s^–1. The present work suggeststhat OH-initiated oxidation of N-methylethaniminemay generate intermediates that could contribute to acetaldehyde formationthrough subsequent oxidation steps in interstellar environments andprovides mechanistic insight into the possible role of imine oxidationpathways in atmospheric nitrogen chemistry.

Astrochemical models are crucial for explaining molecularabundancesacross diverse astrophysical environments, ranging from the diffuseinterstellar medium to planet-forming protoplanetary disks. However,their success depends on the accurate measurement of key physicalparameters, such as the sticking of gaseous species to dust-grainor ice surfaces; desorption energies (E_d), which indicate how strongly adsorbed species bind to these surfaces;diffusion barriers (E_b), which controlsurface migration; and activation barriers that determine whethertwo adsorbed reactants can react upon encounter. In this review, weexamine the current state of laboratory constraints on these parameters,together with the modeling approaches employed in contemporary astrochemicalstudies. Since interstellar grains are heterogeneous, laboratory studiesuse suitable analogues to approximate their surface composition andmorphology. Experiments show that measured parameters vary widelywith the surface morphology, coverage, ice composition, and experimentalconditions. This makes it difficult to incorporate these parametersinto astrochemical models that simulate the chemical evolution ofastrophysical environments, leading to their underutilization in models.Standard simplifications such as fixed sticking coefficients, constant E_b/E_d ratios, andsingle-valued E_b and E_d values can propagate nonlinearly into model predictions.Finally, we discuss future laboratory requirements, including regime-dependentparametrization, independent measurements of diffusion barriers, andexperiments on astrophysically relevant surfaces and ice compositions,together with modeling approaches that account for parameter distributions,environment-dependent surface properties, and hybrid stochastic-ratetreatments. These developments would provide a more consistent linkbetween microscopic surface processes and the observable chemicalevolution.

An extensive analysis of the high-resolution rotationalspectrum(8–26 GHz, 140–700 GHz, 100–600 cm^–1) of the simplest stable chlorohydrin, 2-chloroethanol, is providedby combining high-resolution infrared, microwave, and millimeter-wavespectra. The ground state and first vibrationally excited state ofboth chlorine isotopologues (HOCH₂CH₂³⁵Cl and HOCH₂CH₂³⁷Cl) are well treatedusing a single-state distorted rotor Hamiltonian in the A reductionand I^r representation, reporting up toa full set of octic distortion constants. The extended microwave spectrumcollected and the well-resolved quadrupole splitting observed thereinallowed for the further refinement of quadrupole coupling parameters.Inclusion of rotationally resolved infrared transitions enabled theaccurate and precise determination of the vibrational band originof ν₂₁ for HOCH₂CH₂³⁵Cl (150.908 599 5 (43) cm^–1). The high spectraldensity made measurement and least-squares fitting of transitionsin both rotational and high-resolution infrared spectra challengingand is the likely source of the larger-than-expected σ_fit value of up to 0.060 MHz for each fit. Nevertheless, the extendedmillimeter-wave spectrum reported here provides spectral frequenciesthat directly overlap with astronomical data, allowing for a morethorough search for this species in the interstellar medium. Despiteits expected formation from HCl with either oxirane or ethylene glycolin the interstellar medium, 2-chloroethanol continues to evade detection.We report upper limits on the column density toward 30 astrophysicallydiverse regions. The reported upper limits do not provide significantnew constraints on the chemistry of this species in the interstellarmedium and highlight the limited knowledge of interstellar chlorinechemistry.

Calcium stannate (CaSnO₃) is a widely usedanalogueof bridgmanite (MgSiO₃), capable of undergoing a pressure-inducedperovskite-to-postperovskite phase transition under accessible experimentalconditions. In this study, high-quality single-crystal CaSnO₃ perovskite was synthesized by solid-state reaction. Its structuralbehavior at pressures up to 50.0 GPa was investigated using diamond-anvilcells combined with in situ synchrotron X-ray diffraction, Raman spectroscopy,and first-principles calculations. X-ray diffraction analysis identifiesthe onset of the phase transition at 17.1 GPa, while Raman spectroscopyprovides complementary evidence through the emergence of a new vibrationalmode at 18.3 GPa. Furthermore, theoretical calculations confirmedthe thermodynamic stability of the postperovskite phase above 17.0GPa, corroborating the experimental findings. Due to its comparableaxial ratio and more readily achievable pressure–temperatureconditions relative to MgSiO₃, CaSnO₃ servesas an excellent low-pressure analogue for elucidating the propertiesand dynamics of the deep Earth’s interior.

Mineral dissolution in multicomponent porous media involvescoupledmineral–water reactions, solute transport, and evolving poretopology. However, most continuum reactive-transport models stillrely on constitutive relations developed for single-mineral media,and the influence of insoluble mineral phases remains poorly understood.Here, we use three-dimensional pore-scale reactive transport simulationsto investigate how the insoluble mineral fraction affects dissolutionpatterns and the evolution of hydraulic and reactive properties. Mineralogicalheterogeneity has regime-dependent effects on dissolution-front stability.At relatively low Péclet numbers, moderate insoluble mineralfractions enhance concentration heterogeneity and promote wormholing,whereas larger fractions disrupt connected reactive pathways and suppressflow focusing. At relatively high Péclet numbers, insolublephases monotonically weaken preferential channel development and drivedissolution toward a more uniform pattern. Mineralogical heterogeneityalso alters permeability evolution. As the insoluble mineral fractionincreases, the permeability–porosity relationship becomes progressivelymore linear in log–log space and approaches a power-law form,while the maximum permeability–porosity exponent decreasesand shows a converging trend. We further find that the reactive surfacearea and bulk dissolution rate can be described by empirical porosity-basedrelationships, which remain consistent across the tested Pécletnumbers, Damköhler numbers, and random mineral distributions.These results improve our understanding of dissolution processes inmineralogically heterogeneous porous media and provide empirical relationshipsfor continuum-scale reactive transport modeling.

The ion-neutral reactionbetween cyanoacetylene (HC₃N) and phenyl anion (C₆H₅^–) leads to the formation of cyanobenzene(C₆H₅CN) and the ethynyl anion (C₂H^–) viaa submerged, exothermic pathway. Through a different mechanism, thesame two reactants also form ethynylbenzene (C₆H₅C₂H) and CN^–. These new reactions canbe a foundation for the production of substituted benzenes using moleculescurrently present on Saturn’s largest moon, Titan. Cyclic aromaticmolecules like C₆H₅CN and C₆H₅C₂H are potential gateways to the formation oflarger complex organic molecules and polycyclic aromatic hydrocarbons(PAHs), and these “monomers″ can lead to the molecularmass growth observed in the Titan atmosphere. A comparison of theanharmonic vibrational spectra of the five multiply substituted reactiveintermediates with that of singly-substituted cyano-PAHs providesa window into the effect of the bonding environment on the vibrationalfrequencies of major functional groups, such as the CN stretchingmotion and aliphatic CH stretches. Reliable rotational parametersfor each intermediate are also computed. These spectral data provideaccurate guidance for future IR and microwave laboratory studies ofthis family of molecules. The data presented here can be useful tothe astrochemical modeling and laboratory astrophysics communities,as interest in Titan continues to grow leading up to the launch ofthe forthcoming Dragonfly mission.

Struvite (NH₄MgPO₄·6H₂O),a wastewater-derived mineral proposed as a slow-release fertilizer,may also influence aqueous photochemical transformations of organicmatter. This study investigates the role of struvite in radical-drivenreactions using a model system containing guaiacyl acetone (GA), alignin-derived phenolic compound, and 3,4-dimethoxybenzaldehyde (DMB),a triplet-state photosensitizer. Photochemical experiments using SolarSimulator combined with electron paramagnetic resonance (EPR) spectroscopyand high-performance liquid chromatography – photodiode arraydetector – electrospray ionization – high-resolutionmass spectrometry (HPLC-PDA-ESI HRMS) analysis reveal that struvitemicrocrystals alter both the radical pool and molecular product distributions.In the presence of struvite, the signal of the 5,5-dimethyl-1-pyrrolineN-oxide (DMPO)-trapped hydroxyl radical (DMPO–OH) decreases,while signals corresponding to DMPOX and the DMPO dimer (associatedwith oxidation and coupling pathways) increase, indicating a redistributionof the radical pool driven by heterogeneous surface interactions.Struvite enhances dimeric product formation, demonstrating its abilityto promote coupling reactions. UV–vis optical measurementsshow a transient ∼5-fold increase in solar-flux-weighted massabsorption coefficients for the GA+DMB+struvite mixture during earlyirradiation stages, driven primarily by increased dimer formation,followed by a decline to values comparable to the struvite-free systemafter 120 min of irradiation. HPLC-PDA-ESI HRMS molecular analysisconfirms enhanced oligomerization and distinct reaction pathways inthe presence of struvite, with evidence for surface-mediated radicalcoupling and potential contributions from ammonium-derived chemistry.These results demonstrate that struvite acts as an active participantin aqueous photochemistry, modifying radical pathways, promoting formationof light-absorbing products, and transiently altering optical properties.The findings suggest that struvite may play a broader role in controllingthe chemical evolution and light absorption of organic matter in naturaland engineered aquatic systems.

To investigate variations in depositional environmentsand organicmatter (OM) enrichment across different tectonic deformation zones,this study analyzed samples from three wells with contrasting deformationintensities: QinX1 (strongly deformed), YF1 (moderately deformed),and QiX1 (weakly deformed). Elemental geochemistry was used to characterizepaleosedimentary environments and mechanisms of OM enrichment. Resultsshow that paleoenvironmental assemblages under different tectonicdeformation regimes significantly influence OM enrichment. Total organiccarbon (TOC) is highest in well QinX1 (mean 4.83%), followed by QiX1(3.26%) and YF1 (1.28%). Ga/Rb–K₂O/Al₂O₃ cross-plots suggest warm-humid deposition for QiX1,arid-cold for QinX1, and transitional climate for YF1. Paleowaterdepth proxies (Fe/Co and Zr/Al) indicate a decreasing water depthgradient from YF1 through QinX1 to QiX1. Redox proxies (U/Th and Ni/Co)indicate predominantly anoxic conditions for QinX1 and YF1, and dysoxicto anoxic conditions for QiX1. Mo/TOC ratios reflect moderate restrictionin QinX1 (mean 16.94), weak restriction in YF1 (68.48), and moderatelystrong restriction in QiX1 (8.41). Paleoproductivity proxy (Ba_bio) shows the highest value in well YF1 (mean 5616.57 μg/g),whereas wells QinX1 (2019.39 μg/g) and QiX1 (2410.13 μg/g)exhibit relatively lower productivity. Terrigenous input proxy (Ti/Al)shows a decreasing trend from YF1 (mean 0.082) through QiX1 (0.061)to QinX1 (0.058). Hydrothermal activity proxy (Co/Zn) exhibits a decreasingtrend from YF1 (mean 0.091) through QinX1 (0.107) to QiX1 (0.136).Comprehensive analysis reveals that the strongly deformed zone (WellQinX1) features low productivity, low dilution and strong preservation;the moderately deformed zone (Well YF1) shows low TOC value characteristicsof high productivity, strong dilution and weak preservation; and theweakly deformed zone (Well QiX1) exhibits balanced enrichment withmoderate productivity, moderate dilution and relatively strong preservation.

The molecular inventory of sulfur-containing speciesin the interstellarmedium remains poorly constrained, particularly for polysulfur organicspecies. Here, a comprehensive ab initio exploration of the C₂H₆S₂ potential energy surface revealsa dense low-energy region containing numerous sulfur-containing structureswith diverse bonding patterns and conformational flexibility. High-leveljun-ChS + VPT2 calculations reproduce the available experimental rotationalconstants with a mean absolute error of approximately 0.2%, providingreliable spectroscopic reference data for future laboratory spectroscopicinvestigations. A total of 57 local minima were identified, includingseven isomers within 30 kcal·mol^–1 of the globalminimum. Ethyl hydrodisulfide and dimethyl disulfide are the moststable structures, whereas geminal and vicinal dithiols remain nearlydegenerate, suggesting that several neutral isomers may be thermodynamicallyaccessible. In contrast to their oxygen analogues, the low-energysulfur isomers exhibit strong energetic crowding and shallow torsionalpotentials, generating large conformational manifolds with temperature-dependentpopulations. Despite this structural diversity, computed ionizationpotentials remain confined to a narrow interval (8.10–9.38eV).

Pyrite sulfur isotopes (δ³⁴S_py) andpyrite sulfur content (S_py) integrate microbial, reservoir,iron, and burial controls, complicating their interpretation in ancientlow-sulfate basins. We combine new paired bulk δ³⁴S_py–δ³⁴S_org and S_py measurements and solid-bitumen reflectance data with Fe-speciationand backscattered-electron (BSE) data previously reported for lateEdiacaran (∼560 Ma) Doushantuo Member IV in the restrictedChengkou sub-basin. Published petrographic observations show commonframboidal pyrite and localized overgrowths of unresolved timing.Equivalent vitrinite reflectance values of 3.48–3.73% indicatethermal overmaturity, but the preserved textures and coherent stratigraphicprofiles support broad retention of a depositional and/or early diageneticpyrite-sulfur signal. In the middle interval, total organic carbon(TOC) covaries positively with δ³⁴S_py andinversely with S_py, while heavier δ³⁴S_py accompanies lower Mo/TOC. The TOC−δ³⁴S_py relationship may reflect both rate-dependent changesin microbial sulfate reduction (MSR) fractionation and progressivedrawdown of a poorly replenished sulfate reservoir. Fe_T/Al and Fe_HR/Al do not increase systematically towardheavier δ³⁴S_py, whereas nonpyritic Fe_HR/Al increases and Fe_py/Fe_HR decreases,showing that a smaller fraction of the operationally defined Fe_HR inventory was converted to pyrite. Concurrently, δ³⁴S_py approaches δ³⁴S_org and Δ³⁴S_org–py narrows. In thisindependently established restricted, low-sulfate setting, the combinedrecords are consistent with an evolving Fe–S co-limitationregime in which sulfate-derived sulfide became increasingly limitingrelative to reactive Fe during progressive reservoir drawdown.