The Journal of Physical Chemistry A最新文献

{"title":"Exploring the Electronic Properties of Cyclic Five-Membered 1,2,3-Triazolium Ions: A Quantum Chemical Study.","authors":"Kanika Manchanda, Nabajyoti Patra, Lahu N Dayare, Prasad V Bharatam","doi":"10.1021/acs.jpca.5c01415","DOIUrl":"https://doi.org/10.1021/acs.jpca.5c01415","url":null,"abstract":"<p><p>Cyclic nitrenium ions (CNIs) are generally stable and have found applications in chemistry, including biochemistry. Cyclic five-membered 1,2,3-triazolium ions (CFTIs) are a special class of CNIs; such moieties are found in a few medicinally important species. Though they are isoelectronic to N-heterocyclic carbenes (NHCs), they exhibit electrophilic properties (unlike nucleophilic NHCs). A few quantum chemical studies were reported, but extensive study on CFTIs is required to understand their electronic features and design species with tailored electronic properties. In this work, a thorough quantum chemical analysis has been carried out on the standard CFTI (1,3-dimethyl-1,2,3-triazolium ion). Hydride ion affinity and fluoride ion affinity parameters were estimated to evaluate the Lewis acidic character of the CFTIs. Also, the electrophilicity of these species has been estimated in terms of global electrophilicity index (ω) values. The complexation energies of CFTIs with PMe₃ (Δ<i>H</i>_PMe₃) and 1,3-dimethylimidazol-2-ylidene (Δ<i>H</i>_NHC) have also been estimated. The modulation of the electronic properties of CFTIs as a function of substitution and ring fusion has been evaluated. The correlation between Δ<i>H</i>_PMe₃ and Δ<i>H</i>_NHC is very high (<i>R</i> = 0.99); this correlation helps in identifying CFTIs that may exhibit high Lewis acidic character.</p>","PeriodicalId":59,"journal":{"name":"The Journal of Physical Chemistry A","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2025-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144085573","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"H Atom Abstractions from C₁-C₄ Alcohols, Aldehydes, and Ethers by NO₂: <i>Ab Initio</i> and Comprehensive Kinetic Modeling.","authors":"Hongqing Wu, Ruoyue Tang, Yuxin Dong, Xinrui Ren, Mingrui Wang, Ting Zhang, Song Cheng","doi":"10.1021/acs.jpca.5c00179","DOIUrl":"https://doi.org/10.1021/acs.jpca.5c00179","url":null,"abstract":"<p><p>As crucial additives and intermediates, alcohols, ethers, and aldehydes play significant roles in the combustion process. However, the chemistry of NO_X/hydrocarbon interactions and the rate rules governing these interactions remain largely unexplored in this combustion system. To address this gap, this study provides a comprehensive investigation of H atom abstraction by NO₂ from C₁-C₄ alcohols, aldehydes, and ethers that leads to the formation of three HNO₂ isomers (i.e., <i>trans</i>-HONO, HNO₂, and <i>cis</i>-HONO), encompassing nine hydrocarbons and over 50 reactions. Utilizing the DLPNO-CCSD(T)/cc-pVDZ//M06-2<i>X</i>/6-311++g(d,p) method, the electronic structures, single-point energies, C-H bond dissociation energies, and 1D hindered rotor potentials of the reactants, transition states, complexes, and products in each reaction are computed. The potential energy surfaces and energy barriers for each reaction are determined based on these calculations. Subsequently, the rate coefficients for all studied reactions are derived using transition state theory, implemented with the Master Equation System Solver program, across a temperature range from 298.15 to 2000 K. A thorough analysis of branching ratios highlights the differences and similarities between species, HNO₂ isomers, and abstraction sites, leading to the establishment of consistent rate rules that can be used for rate estimation by analogy for a wider range of oxygenated species. Adding these H atom abstractions to the chemical kinetic model improves the model reactivity and advances the ignition, as indicated by the reduction in the ignition delay time for species that initially lacked these reactions. Further sensitivity and flux analyses highlight the crucial role of H atom abstraction by NO₂. The findings underscore the importance of accurately incorporating these kinetic parameters into newly developed chemical models for alcohols, aldehydes, and ethers. Additionally, this study highlights the need for future experimental efforts to investigate the effects of NO₂ on the combustion systems of these compounds.</p>","PeriodicalId":59,"journal":{"name":"The Journal of Physical Chemistry A","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2025-05-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144074934","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Ab Initio Kinetics for Hydrogen Abstraction from Aldehydes and Alcohols by CH₃Ȯ Radicals.","authors":"Mengmeng Jia, Xuan Ren, Jiaxin Xie, Ruoyue Tang, Song Cheng, Fang Wang, Shuyuan Liu, Daming Zhou, Yang Li","doi":"10.1021/acs.jpca.5c01163","DOIUrl":"https://doi.org/10.1021/acs.jpca.5c01163","url":null,"abstract":"<p><p>The process of hydrogen abstraction by methoxy radicals (CH₃Ȯ) represents a fundamental reaction class in hydrocarbon combustion chemistry, playing a pivotal role in fuel decomposition kinetics and radical chain propagation mechanisms. The reaction rate constants for hydrogen abstraction from C₁-C₂ aldehydes and C₁-C₃ alcohols by CH₃Ȯ radicals are systematically studied by using high-level quantum chemical calculations. Geometry optimization, determination of vibrational frequency, and dihedral angle scans are conducted with the M06-2<i>X</i>/6-311++G(d,p) approach. The QCISD(T)/cc-pVXZ (X = D, T) and MP2/cc-pVXZ (X = D, T, and Q) levels of theory are employed for calculating the single-point energies. Rate constants are derived using transition-state theory, which incorporates quantum mechanical effects, while the thermochemical properties are obtained through statistical thermodynamics. Rate comparisons are conducted for abstracting hydrogen from different sites for a given molecule and from a specific site in different molecules. All computational results are subsequently integrated into the NUIGMech1.3 model to evaluate their impact on the prediction of ignition delay times (IDTs). The results indicate that the newly introduced thermodynamic and kinetic parameters have a significant effect on the IDTs of NC₃H₇OH and IC₃H₇OH. Sensitivity and flux analyses are conducted to determine the essential reactions that govern the observed phenomena.</p>","PeriodicalId":59,"journal":{"name":"The Journal of Physical Chemistry A","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2025-05-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144074860","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Exploring the Effects of Fluorination at the Central Unit of Y6-Type Nonfullerene Acceptors on Photovoltaic Properties: A Computational Investigation.","authors":"Zhiyun Chen, Shaohui Zheng","doi":"10.1021/acs.jpca.5c02299","DOIUrl":"https://doi.org/10.1021/acs.jpca.5c02299","url":null,"abstract":"<p><p>The strategy of modification of central units of Y6-type nonfullerene acceptors (NFAs) with halogenation has become popular for designing new photovoltaic materials and has shown dramatic effects in improving photovoltaic properties. However, the underlying mechanism of how halogenation of central units of these NFAs influences photoelectric properties remains rather elusive. In this paper, focusing on two reported promising NFAs <b>Qx-1</b> and <b>Qx-2,</b> with varying degrees of ring fusion at central units, we designed 4 new NFAs and modeled 10 NFAs systematically through fluorination at the central units. Using density functional theory (DFT) and time-dependent DFT calculations, we explore the impact of an altered fluorinated location at the central units of <b>Qx-1</b> and <b>Qx-2</b> on the photoelectric properties. The molecular planarity, dipole moment, electrostatic potential (ESP) and its fluctuation, exciton binding energy (<i>E</i>_b), singlet-triplet energy gap, and absorption spectrum are obtained with combinations of traditional hybrid or long-range corrected density functionals and Pople basis sets. We also developed a new numerical method to analyze the fluctuation of ESP quantitatively because recent reports discussed its importance. The computed data suggest that newly designed <b>Qx2-bf</b> and <b>Qx2-cf</b> are promising NFAs because they exhibit enhanced planarity, lower <i>E</i>_b (by at least 0.002 eV), and higher averaged ESP (by at least 0.247 kcal/mol) compared to <b>Qx-2</b>. We also find that fluorination of the core units reduces <i>E</i>_b noticeably, increases the ESP standard deviation, and raises the average ESP except for ortho (outside) substitutions. These findings offer valuable physical insights into the effects of core fluorination, which can serve as a guide for the rational design of high-performance QX-based NFAs.</p>","PeriodicalId":59,"journal":{"name":"The Journal of Physical Chemistry A","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2025-05-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144074933","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A Theoretical Kinetic Study of Nitrocyclohexane Combustion: Thermal Decomposition Behavior and H-Atom Abstraction.","authors":"Siyu Cheng, Yinjun Chen, Frederick Nii Ofei Bruce, Xuan Ren, Shuyuan Liu, Zhiwu Wang, Yang Zhang, Yang Li","doi":"10.1021/acs.jpca.4c05887","DOIUrl":"10.1021/acs.jpca.4c05887","url":null,"abstract":"<p><p>Nitrocyclohexane (NCH) is regarded as a highly promising energetic liquid fuel and additive for pulse detonation engines (PDEs) due to its excellent ignition performance and rapid energy release characteristics. Developing a detailed kinetic model for NCH is crucial for understanding its combustion characteristics and accurately predicting its behavior under actual operating conditions. In this study, reactive molecular dynamics (RMD) simulations were performed employing the <i>ReaxFF-lg</i> force field and the canonical (NVT) ensemble to investigate the temperature-dependent kinetic behavior of NCH. The results indicate that the initial decomposition of NCH is primarily driven by C-N bond rupture, followed by C-H bond cleavage, H atom abstraction, and other reactions, with H-abstraction playing a more significant role at lower temperatures. Subsequently, a systematic investigation of H-abstraction at seven sites in NCH involving six small species (Ḣ, ȮH, ĊN, HȮ₂, NO₂, and O₂) was conducted at the QCISD(T)/cc-pVXZ(X = D,T)//MP2/cc-pVXZ (X = D,T,Q)//M06-2X/6-311++G(d,p) level of theory. The calculations reveal that there are minimal differences in reactivity between axial and equatorial H-abstraction, which proceed as parallel reaction channels. Compared to H-abstraction at nitro-substituted, meta, and para positions on the NCH ring, ortho H-abstraction reactions exhibit relatively lower rate coefficients. The obtained kinetic parameters in Arrhenius form and thermodynamic data in NASA polynomial format, covering a wide temperature range (298.15-2000 K), can be directly utilized for the development of the NCH kinetic mechanism.</p>","PeriodicalId":59,"journal":{"name":"The Journal of Physical Chemistry A","volume":" ","pages":"4175-4188"},"PeriodicalIF":2.7,"publicationDate":"2025-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143951525","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Correction to \"Association Kinetics for Perfluorinated <i>n</i>-Alkyl Radicals\".","authors":"Hrishikesh Ram, Yuri Georgievskii, Sarah N Elliott, Stephen J Klippenstein","doi":"10.1021/acs.jpca.5c02616","DOIUrl":"10.1021/acs.jpca.5c02616","url":null,"abstract":"","PeriodicalId":59,"journal":{"name":"The Journal of Physical Chemistry A","volume":" ","pages":"4337-4338"},"PeriodicalIF":2.7,"publicationDate":"2025-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143951608","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Parahydrogen-Hyperpolarized Propane-<i>d</i>₆ Gas Contrast Agent: <i>T</i>₁ Relaxation Dynamics and Pilot Millimeter-Scale Ventilation MRI.","authors":"Nuwandi M Ariyasingha, Clementinah Oladun, Anna Samoilenko, Md Raduanul H Chowdhury, Shiraz Nantogma, Zhongjie Shi, Kehuan Luo, Sidhartha Tan, Oleg G Salnikov, Alba Xhupi, Majd Suleiman, Yuri A Chekmenev, Larisa M Kovtunova, Igor V Koptyug, Juri G Gelovani, Boyd M Goodson, Eduard Y Chekmenev","doi":"10.1021/acs.jpca.4c08800","DOIUrl":"10.1021/acs.jpca.4c08800","url":null,"abstract":"<p><p>Hyperpolarized (HP) MRI provides enhanced signals over conventional MRI due to the increase in nuclear spin polarization by orders of magnitude compared to thermal polarization. Therefore, HP MRI can be successfully utilized toward imaging of low-density gases in void spaces, such as human lungs. Specifically, in clinical pulmonary imaging, HP MRI employs a gaseous contrast agent that fills the lungs during inhalation under physiologically relevant conditions prior to imaging. FDA-approved HP ¹²⁹Xe gas can now be used as the first HP inhalable gaseous contrast agent for functional lung imaging in adults and pediatric patients above 12 years for diagnosis and monitoring responses to the treatment of many pulmonary diseases. However, despite the substantial success of HP ¹²⁹Xe in research settings, the production and MRI of this novel contrast agent remain expensive and not universally available on clinical MRI scanners. An alternative approach is to deploy a proton-hyperpolarized gas that is cheap and fast to produce and can be detected on any clinical MRI scanner without any modification. Hyperpolarized propane gas has recently emerged as a potential next-generation hyperpolarized inhalable contrast agent. Here, the relaxation dynamics of two deuterated hyperpolarized propane isotopologues have been explored at clinically relevant conditions of 1 atm gas pressure and 0.35 and 1.4 T magnetic fields using pairwise addition of parahydrogen to a corresponding unsaturated precursor over the heterogeneous Rh/TiO₂ catalyst. The <i>T</i>₁ relaxation time of HP propane-<i>d</i>₆ gas (0.91±0.03 s) at 1.4 T was found to be similar to that of HP propane gas (0.81±0.06 s) because the dominating relaxation mechanism is due to the coupling of the nuclear spins to the molecular rotation of these two propane gas isotopologues. Moreover, the effective polarization decay constant increases for HP propane-<i>d</i>₆ to 1.35±0.05 s (and for HP propane to 1.35±0.10 s) at 0.35 T, pointing to the likely \"partial\" presence of the long-lived spin states (LLSS) at this clinically relevant field, corresponding to the intermediate spin-spin coupling regime of the two parahydrogen-derived hyperpolarized sites. Furthermore, the pilot feasibility of rapid lung ventilation imaging with 1 × 1 × 9 mm² voxel-size spatial resolution using a clinical 0.35 T open MRI scanner was demonstrated by inflating HP propane-<i>d</i>₆ gas in excised rabbit lungs, despite the reduction of the HP gas relaxation constant to 0.78 ± 0.02 s in the lungs.</p>","PeriodicalId":59,"journal":{"name":"The Journal of Physical Chemistry A","volume":" ","pages":"4275-4287"},"PeriodicalIF":2.7,"publicationDate":"2025-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143952714","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Photophysics of a Methylated GFP Chromophore Anion in Vacuo.","authors":"Thomas Toft Lindkvist, Christian Sillesen, Nikolaj Klinkby, Henrik H Jensen, Lars H Andersen, Steen Bro Ndsted Nielsen","doi":"10.1021/acs.jpca.5c02039","DOIUrl":"10.1021/acs.jpca.5c02039","url":null,"abstract":"<p><p>The photophysical properties of the isolated chromophore anion from the green fluorescent protein have been extensively studied over the years to understand the factors influencing transition energies, excited-state lifetimes, and fluorescence. A commonly used model for the protein chromophore is <i>4'-hydroxybenzylidene-2,3-dimethyl-imidazolinone</i> (<i>p</i>-HBDI). In this work, we have spectroscopically characterized a derivative, brMe-<i>p</i>-HBDI, which features methylation on the carbon bridging the phenol and imidazolinone rings. Experiments were conducted on the anionic form in the gas phase and at cryogenic temperatures using the SAPHIRA ion-storage ring and the LUNA2 fluorescence mass spectrometer, both located in Aarhus. Photoinduced action spectra reveal that brMe-<i>p</i>-HBDI^- cooled to about 20-30 K exhibits maximum absorption at 496.0 ± 0.5 nm. Vibrationally resolved bands appear at shorter wavelengths, while a featureless absorption tail extends toward longer wavelengths, up to approximately 520 nm. The methyl substituent induces a clear redshift (75 meV) in absorption as <i>p</i>-HBDI^- absorbs maximally at 481.51 ± 0.15 nm. The excited-state lifetime of brMe-<i>p</i>-HBDI^- is determined to be 51 ± 3 ps following 495 nm photoexcitation and probing at 800 nm, which is significantly shorter than the nanosecond lifetime previously reported for <i>p</i>-HBDI^-. Consistent with this, no fluorescence was detected from brMe-<i>p</i>-HBDI^- at 100 K, in contrast to <i>p</i>-HBDI^- that is strongly fluorescent according to recent work. These findings are corroborated by (time-dependent) density-functional theory calculations: A methyl substituent at the bridge carbon is predicted to cause a redshift of 77 meV, in excellent agreement with the experimental shift. We find that brMe-<i>p</i>-HBDI^- is planar in the ground state (S₀) but undergoes a twist motion in the S₁ state, leading to a lower-energy nonplanar form where the angle between the two rings is 90°. Our work reveals that even a minor alteration in molecular structure can have a significant impact on the photophysics.</p>","PeriodicalId":59,"journal":{"name":"The Journal of Physical Chemistry A","volume":" ","pages":"4245-4251"},"PeriodicalIF":2.7,"publicationDate":"2025-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143952823","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Complex-Variable Equation-of-Motion Coupled-Cluster Singles and Doubles Theory with the Resolution-of-the-Identity Approximation.","authors":"Simen Camps, Cansu Utku, Joel Creutzberg, Thomas-C Jagau","doi":"10.1021/acs.jpca.5c01313","DOIUrl":"https://doi.org/10.1021/acs.jpca.5c01313","url":null,"abstract":"<p><p>We present an implementation of complex-variable equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) theory with the resolution-of-the-identity (RI) approximation. Complex-variable methods are used in the framework of non-Hermitian quantum chemistry to treat electronic resonances. As test cases, we study different types of resonances of N₂ and CO, namely, temporary anions, Stark resonances, autoionizing Rydberg states, and core-ionized states that decay by the Auger-Meitner effect. Temporary anions are treated with the complex basis function (CBF) method and different variants of the complex absorbing potential method. The other resonances are treated only with CBFs. The memory requirements of our implementation are significantly lower than those of canonical EOM-CCSD. We demonstrate that the RI error is smaller than the basis set error for all types of resonances. However, when the size of the decay width approaches the magnitude of the RI error, the width is qualitatively wrong with the RI approximation. In addition, when an adequate auxiliary basis set is not available, i.e., for autoionizing Rydberg states and for core-ionized states, the RI error in the total decay width increases by a factor 10.</p>","PeriodicalId":59,"journal":{"name":"The Journal of Physical Chemistry A","volume":" ","pages":""},"PeriodicalIF":2.7,"publicationDate":"2025-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144074881","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mechanistic Foundations of the Sequential Activation of Methane by Ta⁺: Oxidative Addition, Ring-Opening σ-Bond Metathesis, and C-C Bond Formation.","authors":"Tucker W R Lewis, Albert A Viggiano, Brendan C Sweeny, Jennifer Meyer, Shaun G Ard, Nicholas S Shuman","doi":"10.1021/acs.jpca.5c01569","DOIUrl":"10.1021/acs.jpca.5c01569","url":null,"abstract":"<p><p>The kinetics of Ta⁺ + CH₄ and related reactions TaC<i>_n</i>H<i>_m</i>⁺ + CH₄ (<i>n</i> = 2-4, <i>m</i> = <i>n</i>, 2<i>n</i>, 3<i>n</i>) are measured from 300-600 K using a selected-ion flow tube apparatus. Complicated kinetics are analyzed through a novel bootstrapping methodology, and rate constants for 38 unimolecular, bimolecular, and ternary processes are reported at each of the four temperatures. As has been well-established, Ta⁺ efficiently dehydrogenates methane through a non-spin-conserved process. Sequential chemistry leads to the dehydrogenation of up to four methane molecules per tantalum center through the competing processes of TaC<i>_n</i>H<i>_m</i>⁺ + CH₄ → TaC_<i>n</i>+1H_<i>m</i>+2⁺ + H₂ (dehydrogenation) and TaC_<i>n</i>+1H_<i>m</i>+4⁺ (association). Supported by density functional theory calculations, the distinct mechanisms and product structures of the sequential reactions are derived. The activation energy for oxidative insertion of Ta into a C-H bond is well-predicted by a simple heuristic: whether or not the reactant tantalum atom possesses unbound valence electrons of opposite spin. TaCH₂⁺ is predicted to have a small activation energy for oxidative insertion but can only proceed to dehydrogenation of methane via carbon-carbon bond formation, enabled by three separate intersystem crossing events. The product is determined to be the tantalapropene dihydride cation, not the more intuitive tantalapropane cation, via comparison of measured and calculated thermal dissociation rates. The TaC₂H₄⁺ tantalapropene dihydride has a prohibitive barrier to oxidative insertion. It proceeds instead through a ring-opening insertion of the entire tantalapropene moiety into a C-H bond via σ-bond metathesis; the unbroken metallacycle bond acts as a tether, preventing the activated products from separating and allowing for further isomerization, leading to dehydrogenation. This and subsequent dehydrogenation processes occur without carbon-carbon bond formation; no evidence of a tantalabutane or larger metallacycle is found.</p>","PeriodicalId":59,"journal":{"name":"The Journal of Physical Chemistry A","volume":" ","pages":"4217-4233"},"PeriodicalIF":2.7,"publicationDate":"2025-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143955055","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}