Tucker W. R. Lewis, Shaun G. Ard, Albert A. Viggiano, Nicholas S. Shuman, Wuhu Feng, John M. C. Plane
{"title":"Ion–Molecule Chemistry Relevant to Iodine in the Upper Atmosphere","authors":"Tucker W. R. Lewis, Shaun G. Ard, Albert A. Viggiano, Nicholas S. Shuman, Wuhu Feng, John M. C. Plane","doi":"10.1021/acsearthspacechem.6c00175","DOIUrl":"https://doi.org/10.1021/acsearthspacechem.6c00175","url":null,"abstract":"<p>Thekinetics of I<sup>+</sup> + O<sub>3</sub>, IO<sup>+</sup> +O<sub>3</sub>, and IO<sup>+</sup> + O are measured using a selected-ionflow tube apparatus over the range of 160–300 K. Recommendedrate constants (cm<sup>3</sup> s<sup>–1</sup>) are: I<sup>+</sup> + O3 <em>k</em> = 8.9 ± 1 × 10<sup>–10</sup> (<em>T</em>/200 K)<sup>−0.15</sup>; IO<sup>+</sup> + O<sub>3</sub><em>k</em> = 8 ± 2 × 10<sup>–11</sup>; IO<sup>+</sup> + O <em>k</em> = 1.6 ± 0.5 × 10<sup>–10</sup> (<em>T</em>/200 K)<sup>−2</sup> cm<sup>3</sup> s<sup>–1</sup>. The IO<sup>+</sup> + O<sub>3</sub> reaction yields primarily IO<sub>2</sub><sup>+</sup> + O<sub>2</sub>, with an upper limit on I<sup>+</sup> + 2O<sub>2</sub> of 10<sup>–11</sup> cm<sup>3</sup> s<sup>–1</sup>. The resultsare supported by density functional calculations. A previously reportedimplementation of iodine chemistry using the Whole Atmosphere CommunityClimate Model is updated with these values and the chemistry of iodinein the upper atmosphere is discussed.</p>","PeriodicalId":15,"journal":{"name":"ACS Earth and Space Chemistry","volume":"10 9","pages":"2085–2093"},"PeriodicalIF":2.6,"publicationDate":"2026-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148985308","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Amber E. Birt, Daniel Ammer, Felix E. Agblemanyo, Andrew S. Wozniak, Amanda A. Frossard
{"title":"Distinct Lipid Compositions in Seawater and the Sea Surface Microlayer Measured with Liquid Chromatography and High-Resolution Mass Spectrometry","authors":"Amber E. Birt, Daniel Ammer, Felix E. Agblemanyo, Andrew S. Wozniak, Amanda A. Frossard","doi":"10.1021/acsearthspacechem.6c00084","DOIUrl":"https://doi.org/10.1021/acsearthspacechem.6c00084","url":null,"abstract":"<p>The sea surface microlayer (SML) plays an important rolein theair–sea exchange of gases and particles. Surfactants accumulateat and modulate the properties of the SML, but specific chemical andphysical properties driving variability in their distribution in theSML remain unclear. Lipids are a type of surfactant in the ocean andare biomarkers for dissolved organic matter (DOM) sources. We collectedpaired SML and associated subsurface seawater (SSW) samples over threetime points in the North Atlantic Ocean in September 2022 and usedliquid chromatography and high-resolution mass spectrometry (LC–MS)to identify 163 and 189 lipids in the SML and SSW, respectively. Ofthose, just 33 were identified in both layers. Lipids were classifiedas glycolipids, phospholipids, triglycerols, diacylglycerides, monoacylglycerides,and betaine lipids, as well as lipid byproducts, including free fattyacids and polyunsaturated aldehydes. Enrichment factors for each lipidclass show overall enrichment in the SML (average of 1.68 ± 1.43for all classes (<em>n</em> = 28) over all times (<em>n</em> = 3)), varying throughout the day (3.33 ± 4.13 forNight, 0.79 ± 1.76 for Afternoon, and 0.92 ± 1.61 for Evening).Based on these enrichments and ratios of specific lipids, we showthat the SML and SSW are unique microenvironments, with bacteriallipids and degradation products enriched in the SML relative to theSSW. Bacteria and DOM degradation processes may be important for shapingthe lipid and thus surfactant composition in the SML. Determiningthe types of lipids and their sources and degradation processes inthe SML may improve our understanding of the sources and propertiesof surfactants and thus their influence on air–sea exchangeprocesses.</p>","PeriodicalId":15,"journal":{"name":"ACS Earth and Space Chemistry","volume":"10 8","pages":"1870–1883"},"PeriodicalIF":2.6,"publicationDate":"2026-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148810374","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Giuseppe Emanuele Capuano, Riccardo Giovanni Urso, Daniele Fulvio, Giuseppe Antonio Baratta, Carlotta Scirè, Maria Elisabetta Palumbo
{"title":"Correction to “Influence of Interstellar Icy Mantle Composition on Acetaldehyde and Formamide Formation Induced by Low-Energy Cosmic Rays”","authors":"Giuseppe Emanuele Capuano, Riccardo Giovanni Urso, Daniele Fulvio, Giuseppe Antonio Baratta, Carlotta Scirè, Maria Elisabetta Palumbo","doi":"10.1021/acsearthspacechem.6c00257","DOIUrl":"https://doi.org/10.1021/acsearthspacechem.6c00257","url":null,"abstract":"","PeriodicalId":15,"journal":{"name":"ACS Earth and Space Chemistry","volume":"10 8","pages":"1986–1986"},"PeriodicalIF":2.6,"publicationDate":"2026-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148810068","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mishka Rawatlal, Kurt A. M. Spence, Marié E. Smith, Casper Labuschagne, Katye E. Altieri
{"title":"Sources of Water-Soluble Organic Carbon in Aerosols at the Cape Point GAW Station","authors":"Mishka Rawatlal, Kurt A. M. Spence, Marié E. Smith, Casper Labuschagne, Katye E. Altieri","doi":"10.1021/acsearthspacechem.6c00101","DOIUrl":"https://doi.org/10.1021/acsearthspacechem.6c00101","url":null,"abstract":"<p>Aerosols play a majorrole in climate by influencing both radiativeforcing and cloud condensation nuclei (CCN) formation, with organicaerosols comprising a large fraction of the global natural aerosolburden (∼20–70%). Despite this importance, long-termobservations of water-soluble organic carbon (WSOC), particularlyin size-segregated aerosols from natural sources, remain scarce inthe southern hemisphere. Here, we present size-resolved WSOC measurementsfrom an eight-month observational campaign (April to November 2018)at the Cape Point Global Atmosphere Watch (GAW) station, a remotecoastal site at the southern tip of Africa, ideally suited for elucidatingmarine, continental, and mixed aerosol sources. Weekly aerosol sampleswere classified using air mass back trajectories, radon-222 and carbonmonoxide concentrations, wildfire observations, and satellite-derivedchlorophyll-<em>a</em> to assess source influences. Acrossall air mass classifications, WSOC concentrations were consistentlyhigher in the fine mode (<1 μm) than in the coarse mode (>1μm) aerosols (0.58 ± 0.55 μg/m<sup>3</sup> vs 0.20± 0.22 μg/m<sup>3</sup>, respectively). Fine mode WSOCconcentrations were highest during periods influenced by biomass burning(0.87 ± 0.49 μg/m<sup>3</sup>) and continental outflow,while marine and modified marine air masses exhibited lower fine modeWSOC concentrations. However, periods of enhanced marine biologicalactivity were associated with increased fine-mode WSOC concentrations.The observed predominance of WSOC in the fine mode across marine,modified marine, and continental air masses highlights the importanceof secondary formation and atmospheric aging processes, rather thandirect primary emissions, in controlling WSOC concentrations at CapePoint. Overall, WSOC levels at this coastal site reflect an integrationof natural and anthropogenic sources, transport history, and atmosphericprocessing. These results establish a regional baseline for WSOC aerosolsin southern Africa and contribute to a broader understanding of organicaerosol formation in a data-sparse southern hemisphere coastal environment.</p>","PeriodicalId":15,"journal":{"name":"ACS Earth and Space Chemistry","volume":"10 8","pages":"1884–1894"},"PeriodicalIF":2.6,"publicationDate":"2026-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148810453","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Laszlo Nemes, Jos Oomens, Vincent J. Esposito, Vincent Boudon, Alexander G. G. M. Tielens
{"title":"The Computed Microwave Spectrum of the Protonated Fullerene C60H+","authors":"Laszlo Nemes, Jos Oomens, Vincent J. Esposito, Vincent Boudon, Alexander G. G. M. Tielens","doi":"10.1021/acsearthspacechem.6c00110","DOIUrl":"https://doi.org/10.1021/acsearthspacechem.6c00110","url":null,"abstract":"<p>The largest known molecule in the interstellar mediumof galaxies,C<sub>60</sub>, has been detected in its neutral and cationic formthrough its vibrational, UV-driven fluorescence emission spectrumand its electronic absorption spectrum, respectively. The detectionof several polycyclic aromatic hydrocarbon molecules through theirpure rotation spectrum in cold, dense, molecular cloud cores suggeststhat C<sub>60</sub> might be present in these environments as well.The low flux of UV pumping photons in molecular cloud cores and theabsence of suitably bright background stars, make detection of C<sub>60</sub> and its cation through the commonly used methods impractical.As C<sub>60</sub> has no permanent dipole moment, its pure rotationaltransitions are forbidden, and its presence must be inferred fromthe rotational transitions of C<sub>60</sub> derivatives with permanentdipole moments. Here, we present a study of the predicted rotationalspectrum of protonated C<sub>60</sub> that has a sizable permanentdipole moment. Protonation of C<sub>60</sub> reduces the icosahedralsymmetry to C<sub>s</sub> and results in a dipole moment of about3.8 D. The resulting C<sub>60</sub>H<sup>+</sup> is a closed shellsystem with no electron spin. The ground electronic symmetry is A’.The goal of the present calculations is to simulate rotational spectrain radio astronomy frequency ranges. The simulations are based ongeometry and electric dipole moment values from harmonic and anharmonicdensity functional theory (DFT) calculations at the B3LYP level. Usingthe PGOPHER spectral simulation program, the rotational structureof the spectra at excitation temperatures of 5 and 10 K were computedto guide future laboratory studies and facilitate radio astronomysearches for protonated C<sub>60</sub> in cold dark molecular clouds.</p>","PeriodicalId":15,"journal":{"name":"ACS Earth and Space Chemistry","volume":"10 8","pages":"1938–1946"},"PeriodicalIF":2.6,"publicationDate":"2026-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148810209","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Xi Zhang, Andreas Kappler, Qian Tian, Jie Jiang, Zhen Yang, Tian ran Sun
{"title":"Electron Transfer Reversibility of Mineral-Associated Organic Matter Dominated by Redox-Active Metastable Substances in a Wetland–Grassland Transition Zone","authors":"Xi Zhang, Andreas Kappler, Qian Tian, Jie Jiang, Zhen Yang, Tian ran Sun","doi":"10.1021/acsearthspacechem.6c00141","DOIUrl":"https://doi.org/10.1021/acsearthspacechem.6c00141","url":null,"abstract":"<p>Soil organic matter is redox-active, capable of respondingto redoxfluctuations, and acts as a biogeobattery to facilitate biogeochemicalcycling. However, whether the electron-transfer capacities of mineral-associatedorganic matter (MAOM) are reversible under controlled chemical redox-switchingconditions remains unclear. Mediated electrochemical reduction/oxidation(MER/MEO) analysis showed that MAOM from the transition zones (e.g.,between wetland and grassland ecosystems) exhibited the highest electron-acceptingand -donating capacities (EAC and EDC) and reversible electron transfercapacity under varying redox states. Specifically, when conditionsshift from oxidizing to reducing, the EAC of MAOM decreased in tandemwith an equivalent increase in EDC. Conversely, when conditions revertto oxidizing, EAC increased while EDC decreased, demonstrating a fullyreversible electron transfer behavior. Multiple complementary analysesreveal that MAOM in the transition zone was enriched in redox-activemetastable phases (RAMPs), including redox-active carboxyl functionalgroups and mineral phases. Mineral phases were the major source oftotal electron exchange capacity (EEC), whereas organic matter functionedas an important modulator of coupled redox dynamics. MAOM featuresco-occurrences of iron–carbon (Fe–C) covalent bondingand abundant carboxyl functional groups, as well as mixed-valenceiron phases (e.g., green rust and magnetite) and poorly crystallineiron (oxyhydr)oxide minerals (e.g., ferrihydrite and goethite), allof which contribute to electron transfer reversibility. These resultssuggest that MAOM contains RAMPs that support electron transfer reversibilityunder varied redox conditions, thereby influencing the overall biogeochemistryand persistence of the soil ecosystem.</p>","PeriodicalId":15,"journal":{"name":"ACS Earth and Space Chemistry","volume":"10 8","pages":"1964–1973"},"PeriodicalIF":2.6,"publicationDate":"2026-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148810032","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Oxalate Modulates Cadmium Mobility during Ferrihydrite Transformation: Roles of Dissolution Kinetics and Phase Selection","authors":"Juanjuan Liu, Xiaofan Pan, Ning Deng, Xin Huang","doi":"10.1021/acsearthspacechem.6c00109","DOIUrl":"https://doi.org/10.1021/acsearthspacechem.6c00109","url":null,"abstract":"<p>Cadmium (Cd) mobility is strongly influenced by ferrihydrite(Fh)transformation, and low-molecular-weight organic acids (LMWOAs) canmodulate this process and thereby alter the Cd<sup>2+</sup> environmentalfate. However, the mechanisms by which organic ligands control Fhtransformation and consequently influence Cd<sup>2+</sup> behaviorremain poorly understood. Here, we investigated Fh transformationand the associated fate of Cd<sup>2+</sup> in the presence of oxalicacid (Ox), an organic ligand ubiquitous in natural environments. Resultsshowed that Ox significantly increased Cd<sup>2+</sup> release kineticsby accelerating Fh dissolution through coupled surface inner-spherecomplexation and aqueous Fe<sup>3+</sup>-oxalate complexation. Oxalso reduced the surface energy of hematite (Hm) from ∼340to ∼183 mJ/m<sup>2</sup>, which increased the nucleation rateratio of Hm to goethite (Gt) from ∼1.70 to ∼90.92. Thisshift promoted the preferential formation of Hm, which reduced theavailability of reactive surface sites for Cd<sup>2+</sup> readsorptionand thereby increased the overall release extent. At growth stage,Ox altered Hm growth pathways from classical ion-by-ion growth toparticle-mediated aggregation, facilitating the physical encapsulationof solid-associated Cd<sup>2+</sup> and enhancing its stabilizationin nonextractable forms. These findings demonstrated that Ox exerteda dual control on Cd<sup>2+</sup> environmental behavior by promotingboth its release and subsequent sequestration, highlighting the importanceof coupling transformation kinetics, phase selection, and growth mechanismsin predicting the heavy metal fate in organic-rich environments.</p>","PeriodicalId":15,"journal":{"name":"ACS Earth and Space Chemistry","volume":"10 8","pages":"1928–1937"},"PeriodicalIF":2.6,"publicationDate":"2026-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148810408","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Neville J. Curtis, Jason R. Gascooke, Martin R. Johnston, Kirrily C. Rule
{"title":"Proton-Specific Characterization to Explore the Nature of Hydroxyl Hydrogen in Australian Opals","authors":"Neville J. Curtis, Jason R. Gascooke, Martin R. Johnston, Kirrily C. Rule","doi":"10.1021/acsearthspacechem.6c00107","DOIUrl":"https://doi.org/10.1021/acsearthspacechem.6c00107","url":null,"abstract":"<p>Solid-state proton (<sup>1</sup>H) nuclear magnetic resonance(NMR),neutron diffraction (ND) and inelastic neutron scattering (INS) spectraare shown to be distinct for Australian opal-AG, opal-AN and opal-CTsamples. <sup>1</sup>H NMR spectra of opal-AG and opal-AN samplesare strikingly different while both show a trend of increasing protoncontent associated with a peak due to molecular water. Inversion–Recoveryand Dephasing plots reveal additional peaks which may be characterizedby semiquantifiable peak positions, fwhm and relaxation times. Whilepeak assignment is incomplete, results are consistent with the presenceof several examples of molecular water and silanol, including H-bonding.ND and INS spectra do not support the presence of water in sufficientlocal quantities to form ice. INS spectra for opal-AG and opal-CTshow peaks consistent with multiple translational and librationalvibrations indicating “mobile” or “displaceable”protons. Opal-AN samples show less INS activity with little definitionin the spectra. While insights from this work support indicative 2-dimensionalmodels showing interactions between proton-bearing sites, more informationis needed for proposal of 3-dimensional structural models comprisingQ<sub>4</sub>, Q<sub>3</sub> and water components.</p>","PeriodicalId":15,"journal":{"name":"ACS Earth and Space Chemistry","volume":"10 8","pages":"1913–1927"},"PeriodicalIF":2.6,"publicationDate":"2026-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148810143","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Click Chemistry-Enabled Screening of Lignin-Derived Compounds via Non-Targeted Metabolomics","authors":"Sudarshan Basyal, Abrar Shahriar, Anil Timilsina, Alyssa Radakovich, Aiden Berndt, Rene Boiteau, Yuki Tobimatsu, Yu Yang","doi":"10.1021/acsearthspacechem.6c00126","DOIUrl":"https://doi.org/10.1021/acsearthspacechem.6c00126","url":null,"abstract":"<p>Lignin-derived compounds (LDCs) are major contributorsto soilorganic carbon and play a critical role in the global biogeochemicalcycle of carbon. However, the reliable identification of LDCs in complexenvironmental media remains a major analytical challenge. In addition,owing to lignin’s heterogeneous, cross-linked polymeric structure,many LDCs are poorly soluble and exhibit low ionization efficiencyin mass spectrometry, substantially hindering their identification.To overcome these analytical hurdles, we developed an advanced analyticalpipeline integrating click reaction with high-performance liquid chromatography-high-resolutiontandem mass spectrometry (HPLC-HRMS/MS) and nontargeted metabolomicanalysis, enabling the systematic screening and putative identificationof LDCs, including species that are otherwise poorly ionizable orinsoluble. Our study screened LDCs by reacting extractions of azide-taggedlignin polymers with dibenzocyclooctyne-polyethylene glycol acid (DBCO-PEG1).We employed two complementary analytical pathways: (i) targeted massdifference screening of azide-tagging and DBCO-PEG1 adduct, and (ii)diagnostic MS/MS fingerprint analysis based on characteristic fragmentions of DBCO-PEG1. Using this strategy, we screened 17 high-confidencetriplet candidates of LDCs and additional putative candidates identifiedvia MS/MS fingerprinting, spanning a broad chemical space. By integratingclick reaction with HPLC-HRMS/MS and nontargeted metabolomic analysis,this study established a framework for tagging and screening analyticallyinaccessible (“dark”) organic compounds. Further structuralcharacterization of candidate compounds and the application of thisapproach to incubation studies provides a pathway toward improvedmolecular identification of LDCs crucial to soil organic carbon persistence.</p>","PeriodicalId":15,"journal":{"name":"ACS Earth and Space Chemistry","volume":"10 8","pages":"1947–1954"},"PeriodicalIF":2.6,"publicationDate":"2026-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148810307","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Anharmonic Infrared Signatures of C9H7CN Isomers: CN Stretching as a Probe of Cyano-PAHs in the 4.3–4.5 μm Region","authors":"Sayon Satpati, Tarun Roy, Sneha Mridha, Subhas Ghosal","doi":"10.1021/acsearthspacechem.6c00083","DOIUrl":"https://doi.org/10.1021/acsearthspacechem.6c00083","url":null,"abstract":"<p>Recent radio detections of cyano-substituted aromaticmoleculeshave established nitrile functionalization as a powerful observationalauxiliary for identifying polycyclic aromatic hydrocarbons (PAHs)in space. A comprehensive theoretical study of 189 possible nitrileisomers of the molecular formula C<sub>9</sub>H<sub>7</sub><sub>7</sub>CN has been performed to explore the rotational and vibrational spectroscopicsignatures using dispersion-corrected density functional theory (DFT).The cyanoindene derivatives dominate the low-energy region of thepotential energy surface, with 2-cyanoindene identified as the globalminimum. The anharmonic vibrational spectra have been computed usingthe second-order vibrational perturbation theory with explicit treatmentof resonance polyads. Computed composite anharmonic spectra of theseven low-lying isomers show a cluster of strong and confined absorptionbands at 4.367 μm with a narrow width of 0.067 μm originatingfrom the −CN stretching. The intense anharmonic coupling ofthe −CN stretch with proximal combination vibrations manifestsas a distinct, structured spectral band due to Fermi resonances. Thisspectroscopic signature closely mirrors the narrow, high-contrastfeature predicted for larger cyano-PAHs and provides a natural explanationfor the structured baseline and broad emission features observed around∼4.3–4.4 μm in recent near-infrared spectra (NIRSpec)on the <em>James Webb</em> Space Telescope (JWST).</p>","PeriodicalId":15,"journal":{"name":"ACS Earth and Space Chemistry","volume":"10 8","pages":"1855–1869"},"PeriodicalIF":2.6,"publicationDate":"2026-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148810357","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}