Towards a better understanding of the combustion chemistry for prenol and iso-prenol: An ab initio kinetic study on hydrogen abstraction reactions by hydrogen atom

Chemical etch resistance of sputter-deposited metal oxide thin film coatings in atomic hydrogen at 700 °C

Understanding roles of different radicals (·OH, SO4·-and ClO·) in the thiacloprid degradation.

Ascorbate-enabled C-H bond amination catalyzed by myoglobin reconstituted with a trifluoromethyl-substituted Iron porphyrin.

Selective electrocatalytic nitrobenzene-to-aniline reduction on nickel-cobalt layered double hydroxide via dual-site hydrogen atom transfer.

Modelling of nonadiabatic reactions for heterogeneous photocatalysis involving absorbates on metal nanoparticles provides insight for the interpretation of experiments. In this paper, photoinduced H2 dissociation in a Au6H2 model complex has been investigated using Time-Dependent Density Functional Theory (TDDFT), and with a decoherence corrected fewest switches surface hopping (DC-FSSH) approach that includes all degrees of freedom of the Au6H2 cluster in the photodynamics. The excited states of this cluster near the equilibrium geometry mostly involve weakly entangled combinations of transitions between occupied orbitals with 60% gold d-orbital character and unoccupied orbitals that are 95% sp, with little variation between different excited states for energies close to what is the Au plasmon energy for larger clusters. Both adiabatic and nonadiabatic process play significant roles in H-H bond dissociation, with adiabatic dissociation always being fast and nonadiabatic dissociation involving slow or fast mechanisms and little variation in the dissociation dynamics when different excited states are considered. In all cases both hydrogen atoms end up chemisorbed on the Au cluster, in contrast to earlier work which suggested that dissociation was dominated by one or both H atoms going to the gas phase. Most H-H bond dissociation reactions take place via the nonadiabatic pathway and leading to both hydrogens chemisorbed on the nearest Au atom, but others lead to H's on different Au atoms. H2 desorption from the Au6 cluster competes with hydrogen dissociation, and is always nonadiabatic for this model. Charge transfer between the adsorbed H2 molecule and the Au6 cluster is found to make a minor contribution to H-H dissociation. Instead, the calculations show that nonadiabatic transitions between metal localized states are dominant, and that the lowest excited metal-localized state adiabatically evolves into an H2 dissociative state. These calculations provide new insights to an important model system for plasmon mediated photocatalysis.

Abstract The proper time of an observer can be introduced as a degree of freedom in quantum cosmology, additional to the existing fields. We review two arguments for using the Schrödinger equation to evolve the corresponding wavefunction. We restrict to solutions in which time acts as a component with negligible backreaction on the metric -- that is, it plays the role of a test field. We apply this idea to various minisuperspace models. In the semiclassical regime we recover expected results: the wavefunction peaks on the classical solution and, in models with a scalar field, the variance of ζ (a mini-superspace analogue of the comoving curvature perturbation) is conserved. Applied to the no-boundary wavefunction, our model recovers the bouncing behavior of classical global de Sitter space, with small corrections associated to the evolving variance of the wavefunction. Other bouncing solutions do not have any classical analogue. This is the case of a radiation dominated universe, which classically leads to a big-bang singularity but corresponds quantum mechanically to an 
s-wave scattering off a central potential of the form −r<2><3>. As much as the hydrogen atom, this potential is famously made stable by the Heisenberg uncertainty principle. We study the unitary evolution of the wavepacket numerically. During the bounce, the uncertainty and the expectation value of the scale factor become comparable. By selecting a large initial variance, the bounce can be made arbitrarily smooth, the mean value of the Hubble parameter correspondingly soft.

The photochemistry of UV-irradiated liquid water underlies many physical, chemical, and biological processes, with the formation of the hydrated electron as a central event. Despite extensive experimental and theoretical efforts, its microscopic origin remains incompletely understood. Using excitedstate molecular dynamics simulations of photoexcited liquid water, we resolve the sequence of chemical events leading to hydrated electron formation on the excited state. The excitation localizes on specific hydrogen-bond network defects, followed by two competing pathways. The first produces a hydrogen atom and undergoes ultrafast non-radiative decay to the ground state within 100 femtoseconds. The other proceeds via proton-coupled electron transfer, generating hydronium ions, hydroxyl radicals, and an excitedstate hydrated electron. This mechanism is driven by ultrafast coupled rotational and translational motions of water molecules, forming water-mediated ion-radical pairs that persist on picosecond timescales and influence visible emission. These results provide a unified framework for interpreting time-resolved spectroscopic observations and guide future experimental and theoretical investigations.

Hydrogen atom transfer (HAT) which can produce radical intermediates from alkanes provides a strategy to achieve undirected C(sp 3 )‐H functionalization. Typically, primary CH bonds are the least reactive in HAT processes, compared to tertiary CH or activated benzylic CH. It is noteworthy that HAT‐mediated primary CH functionalization has recently been realized through the adjustment of various factors such as the catalyst or reagent design. This review summarizes recent advances in undirected primary CH functionalization via the HAT process. These examples will be discussed according to the HAT reagent. Reaction conditions, primary selectivity of various substrates, mechanism, and origin of the primary selectivity will be highlighted.

Electrochemical hydrogen production and conversion using renewable energy sources have become a key topic in catalysis research. Platinum and Pt-group metals are among the best materials promoting H2 evolution (HER) and oxidation (HOR) reactions. However, the nature of active surface sites should be further elucidated to improve their performance and gain a better fundamental understanding of those processes. This is not a trivial task, mainly due to the high surface mobility of the H-species. Here, we use in situ electron paramagnetic resonance (EPR) spectroscopy to investigate the Pt surface in the so-called underpotential deposition (UPD) region in acidic media and observe EPR responses indicative of hydrogen adsorption sites, the knowledge of which is essential for both HOR and HER. Our EPR measurements and theoretical ab initio molecular dynamics (AIMD) calculations suggest that the average adsorption sites for atomic hydrogen at the surface of platinum are either on-top sites or 3-fold hollow sites, while bridge sites are not likely to be occupied. For EPR, the intensity maximum is reached at -0.85 V versus Pt, and then the signal intensity vanishes for potentials just before HER, suggesting EPR-silent H2 formation. At the same time, ab initio density functional theory (DFT) calculations of a Pt(111) surface with 7/12 ML coverage of H at room temperature yield occupancy probabilities of 0.72 (fcc hollow), 0.26 (on-top), and 0 (bridge) for the respective sites. Hence, fcc hollow is favored over on-top adsorption sites at high coverages, which is consistent with the observation via EPR spectroscopy. To our knowledge, EPR spectroscopy was used for the first time to probe the EPR response during hydrogen electrosorption in the HUPD region at polycrystalline platinum electrodes in acidic electrolytes.

Abstract To verify ``hot superconductivity'' recently proposed in lanthanum hydride-based compounds, we explored thermodynamically stable and superconducting phases in the lanthanum (La)-platinum (Pt)-hydrogen (H) ternary system at 20¥,GPa using a computational framework that integrates an evolutionary construction scheme of formation-enthalpy convex hulls, machine learning potential calculations, and density functional theory calculations. Although we found no evidence of the hot superconductivity in this ternary system at the pressure, we predicted a unique compound, LaPtH$_6$. In this compound, PtH$_6$ coordination units are formed, and the hydrogen atoms are arranged in an equilateral triangular pattern that nearly constitutes a two-dimensional kagome lattice between the La and Pt layers, leading to superconductivity at 18.67¥,K. This structure is dynamically stable from ambient pressure to at least 200¥,GPa and the superconducting critical temperature increases from 13.51 to 40.63¥,K.

The source of atmospheric nitrous acid (HONO) has not yet been fully identified, as observed concentrations remain significantly higher than predicted levels. The hydrolysis reaction of t-ONONO2, as a feasible source of HONO, has attracted much attention in the field of atmospheric chemistry. In this study, the roles of sulfuric acid (SA), methanesulfonic acid (MSA), and methyl hydrogen sulfate (MHS) in the hydrolysis reaction of t-ONONO2 to produce HONO and HNO3 were explored by DFT and statistical dynamics methods. Thermodynamic and kinetic data indicate that SA, MHS, and MSA enhance the hydrolysis reaction of t-ONONO2 through two mechanisms: single hydrogen atom transfer (S-HAT) and double hydrogen atom transfer (DHAT). Among these, SA exhibits the strongest catalytic effect. This study will contribute to a better understanding of the mechanistic characterization of t-ONONO2 hydrolysis reactions, which is of great significance for the control of atmospheric particulate matter in polluted areas.

We report a femtosecond time-resolved strong-field study of ammonia borane (AB, BH3NH3) following both single and double ionization, revealing ultrafast fragmentation dynamics and hydrogen release. Time-resolved mass spectrometry and ab initio molecular dynamics simulations are used to identify the molecular origin of the neutral and ionic products. Singly ionized AB produces neutral H and H2, while doubly ionized AB produces neutral H and H2 along with H+, H2+, and H3+, all within 1 ps. Electronic-structure calculations show that H, H+, H2, H2+, and H3+ originate predominantly from hydrogen atoms bound to the boron center and that their formation proceeds through hydrogen migration and, in some channels, neutral H2 roaming. The calculations further indicate that the dication meets the structural and energetic requirements for neutral H2 release, a prerequisite for forming astrochemically relevant H3+. However, the large adiabatic relaxation energy causes most roaming H2 to dissociate before proton abstraction, suppressing H3+ formation. These results provide new insight into dissociative ionization pathways in hydrogen-rich molecules, extend mechanistic principles developed for halogenated alkanes to ammonia borane, and suggest implications for hydrogen-release chemistry in ammonia-borane-based storage materials.

α-Dunnione analogues are regarded as promising candidates for anticancer drug development, while their synthetic methods remain limited. Herein, an efficient Fe(III)-catalyzed hydrogen atom transfer (HAT) strategy is developed for construction of a series of α-dunnione analogues. In this approach, iminophosphorane promotes a reductive radical alkylation to form a quinoid species intermediate, which subsequently undergoes Fe-catalyzed reductive cleavage of the N-P bond and intramolecular cyclization. Among the synthesized derivatives, compounds 3a, 3d, 3e, 3g and α-dunnione exhibits pronounced cytotoxic activity against HepG2 cells. Overall, this study provides an efficient synthetic route to biologically active α-dunnione analogues.

While the ball-milled [Al-Fe-AC]bm composite has demonstrated remarkable performance for nitrate remediation, the underlying mechanisms governing its pH-dependent reactivity and high nitrogen (N2) selectivity remain inadequately elucidated. This work systematically decouples the synergistic roles of Al0, Fe0, and activated carbon (AC) in the [Al-Fe-AC]bm system across a broad pH range (initial pH0 4.0-13.0; stabilized pHw 7.0-12.0). We identify a critical operational pHw threshold of approximately 10.5, beyond which the dominant reduction pathway shifts from direct electron transfer to atomic hydrogen (H*)-mediated reduction. Under acidic to circumneutral conditions, Fe0 corrosion elevates pH to depassivate Al0, enabling electron-driven nitrate reduction with high N2 selectivity (>73%). In contrast, under strongly alkaline conditions, excessive H* generation─promoted by Al//Fe and Al//AC galvanic couples─shifts the pathway toward nonselective hydrogenation, resulting in ammonium as the predominant product, as corroborated by H* scavenging experiments and electrochemical analysis. Strong correlations between AC's specific surface area/pore volume and N2 selectivity, combined with in situ Fourier-transform infrared (FT-IR) detection of *N2O intermediate, demonstrate that AC's nanoconfinement promotes *NO dimerization for selective N-N coupling. This study provides a fundamental mechanistic framework for designing efficient and selective metal-carbon composites for sustainable nitrate remediation.

Abstract Giant low surface brightness (gLSB) galaxies are galaxies with extremely extended, faint, optical disks over 50 kpc in radius and have high total masses, which can reach 10 12 M ⊙ . The existence of such galaxies is problematic for current models of galaxy formation, since the major mergers responsible for the large total mass would likely have destroyed the extended optical disk. Examining the gas content of these galaxies is an important step in determining their formation mechanism, whether it be through slow gas accretion or the large disk (re)forming after a major merger. We present neutral atomic hydrogen (H i ) observations of 19 gLSB galaxies identified with the Hyper Suprime-Cam Subaru Strategic Program survey. Although most have high H i masses, they are generally lower than expected based on their large optical sizes, and we do identify some gLSB galaxies with unusually low gas content. The H i spectra of these galaxies show evidence for a rotational disk, though these disks are more asymmetric than those of other galaxies with comparable mass. Four galaxies with surface brightness profiles similar to those of the gLSB galaxies have also been selected from the Numerical Investigation of a Hundred Astrophysical Objects (NIHAO) simulation for comparison. There is evidence for significant galaxy mergers in the past for three of these NIHAO galaxies, and these three galaxies show similar asymmetry in their H i spectra. Together, these results could indicate that the large optical disk of a gLSB galaxy is the result of a recent merger.

Herein, an aryne-mediated synthesis of sterically hindered arylamines using 2,2,6,6-tetramethylpiperidoxyl (TEMPO) as the amine source is reported. Mechanistic studies suggest that TEMPO adds to the aryne to form an aryl radical, which abstracts a hydrogen atom and then undergoes deoxygenation to afford the arylamine. This unprecedented radical process in aryne chemistry offers a concise route to sterically hindered arylamines.

Abstract. The Great Oxidation Event (GOE) was a 200 Myr transition circa 2.4 billion years ago that converted the Earth's anoxic atmosphere to one where molecular oxygen (O2) was abundant (volume mixing ratio >10-4). This significant rise in O2 is thought to have substantially throttled hydrogen (H) escape and the associated water (H2O) loss. Atmospheric estimations from the GOE onward place O2 concentrations ranging between 0.1 % to 150 % PAL, where PAL is the present atmospheric level of 21 % by volume. In this study we use WACCM6, a three-dimensional Earth System Model to simulate Earth's atmosphere and predict the diffusion-limited escape rate of hydrogen due to varying O2 post-GOE. We find that O2 indirectly acts as a control valve on the amount of hydrogen atoms reaching the homopause in the simulations: less O2 leads to decreased O3 densities that reduce local tropical tropopause temperatures by up to 17 K, which increases H2O freeze-drying and thus reduces the primary source of hydrogen in the considered scenarios. The maximum differences between all simulations in the total H mixing ratio at the homopause and the associated diffusion-limited escape rates are a factor of 3.2 and 4.7, respectively. The prescribed CH4 mixing ratio (0.8 ppmv) sets a minimum diffusion escape rate of ≈2×1010 mol H yr−1, effectively a negligible rate when compared to pre-GOE estimates (∼1012–1013 mol H yr−1). Because the changes in our predicted escape rates are comparatively minor, our numerical predictions support geological evidence that the majority of Earth's hydrogen escape occurred prior to the GOE. Our work demonstrates that estimations of how the tropical tropopause layer and the associated hydrogen escape rate evolved through Earth's history requires 3D chemistry-climate models which include a global treatment of water vapour microphysics.

Covalent organic frameworks (COFs) offer a powerful platform for photocatalysis, yet integrating multiple catalytic functions within a single structure remains challenging. Here, we report the synthesis of dual-functionalized COFs, FeP-Me(AA) and FeP-Me(AB), integrating photosensitizing iron-porphyrin motifs and redox-active iminium linkages, with AA and AB stacking modes controllable through distinct synthetic procedures. Under light irradiation, the COFs efficiently catalyze C-H and alcohol oxidations directly under air at room temperature, without requiring sacrificial reagents. FeP-Me(AA) exhibits superior activity compared to nonmethylated and nonmetalated COF analogues as well as homogeneous catalysts, underscoring the advantages of dual-site integration. Mechanistic studies reveal a bifunctional pathway: the iron-porphyrin units undergo ligand-to-metal charge transfer to generate reactive chlorine or hydroxyl radicals that mediate hydrogen atom transfer to generate carbon-centered radicals, while adjacent iminium linkages transfer electrons to reduce O2 to superoxide radicals. Coordination of these radicals to Fe(III)(TPP) forms an iron(III)-peroxide intermediate, which undergoes subsequent O-O bond cleavage to generate the ketone product. By uniting cooperative functions within a single framework, this work establishes a versatile blueprint for designing sustainable and synergistic photocatalysis with COFs.

Abstract We investigate the evolution of molecular clouds through the kinematics of their atomic hydrogen (H I ) envelopes, using 12 CO and 21 cm emission to trace the molecular and atomic gas, respectively. We measure the large-scale gradients, Ω, in the velocity fields of 22 molecular clouds and their H I envelopes, then calculate their specific angular momenta, j ∝ Ω R 2 . The molecular clouds have a median velocity gradient of 9.6 × 10 −2 km s −1 pc −1 , and a typical specific angular momentum of 2.7 × 10 24 cm 2 s −1 . The H I envelopes have smaller velocity gradients than their respective molecular clouds, with an average of Ω H I = 0.03 km s −1 pc −1 , and a median angular momentum of of j H I ≈ 5.7 × 10 24 cm 2 s −1 . For a majority of the systems, j HI > j H 2 , with an average of j HI / j H 2 = 4 . Their velocity gradient directions tend to be misaligned, indicating that angular momentum is not conserved during molecular cloud formation. Both populations exhibit a j − R scaling consistent with that expected of supersonic turbulence: j H 2 ∝ R 1.67 ± 0.22 , and j H I ∝ R 1.71±0.27 . Combining our measurements with previous observations, we demonstrate a scaling of j ∝ R 1.50±0.02 in star-forming regions spanning 5 dex in size, R ∈ (10 −3 , 10 2 ) pc. We construct a model of angular momentum transport during molecular cloud formation, and derive the angular momenta of the progenitors to the present-day systems. We calculate a typical angular momentum redistribution timescale of 13 Myr, comparable to the H I envelope free-fall times.