Dissociation Dynamics Research Articles

High-Entropy Perovskite (Pr1/6Nd1/6Sm1/6Ba1/6Sr1/6)6/7(Mn1/6Co)6/7O3-δ as a Highly Active and CO2 Durable Cathode for Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are environmentally friendly energy conversion devices that convert the chemical energy in fuels directly into electrical power. The development of high-catalytic activity and durability cathode materials is crucial for the commercialization of SOFCs. Herein, a novel A-site deficient high-entropy perovskite oxide (Pr1/6Nd1/6Sm1/6Ba1/6Sr1/6)6/7(Mn1/6Co)6/7O3-δ (PNSBSMC) was designed. The strong disorder effect associated with entropy increase in high-entropy perovskite oxide is anticipated to accelerate oxygen reduction reaction (ORR) kinetics. PNSBSMC demonstrates excellent catalytic activity for oxygen reduction, primarily due to the entropy-driven enhancement that promotes oxygen adsorption, dissociation, and charge transfer dynamics. The increase in entropy not only significantly mitigates the thermal expansion of PNSBSMC but also provides additional pathways for ionic/electronic transport. At 800 °C, the PNSBSMC-based single cell achieved a remarkable peak power density of 1.41Wcm-2, representing an 88.0% improvement over the single-phase PBC. Additionally, PNSBSMC demonstrates superior performance stability and CO2 tolerance. These findings suggest that high-entropy PNSBSMC perovskite holds significant potential as an effective cathode for SOFCs. This study offers new insights for the future development of high-stability, high-activity SOFC cathode materials.

Observation of sequential three-body dissociation of camphor molecule—a native frame approach

Abstract The three-body dissociation dynamics of the dicationic camphor molecule (C10H16O2+) resulting from Auger decay are investigated using soft x-ray synchrotron radiation. A photoelectron-photoion-photoion coincidence method, a combination of a velocity map imaging spectrometer and a time-of-flight spectrometer is employed to measure the 3D momenta of ions detected in coincidence. The ion mass spectra and the ion–ion coincidence map at photon energies of 287.9 eV (below the C 1s ionization potential) and 292.4 eV (above the C 1s ionization potential for skeletal carbon) reveal that fragmentation depends on the final dicationic state rather than the initial excitation. Using the native frame method, three new fragmentation channels are discussed; (1) CH2CO+ + C7H 11 + + CH3, (2) CH 3 + + C7H 11 + + CH2CO, and (3) C2H 5 + + C6H 9 + + CH2CO. The dominating nature of sequential decay with deferred charge separation is clearly evidenced in all three channels. The results are discussed based on the experimental angular distributions and momenta distributions, corroborated by geometry optimization of the ground, monocationic, and dicationic camphor molecule.

Few-femtosecond time-resolved study of the UV-induced dissociative dynamics of iodomethane

Ultraviolet (UV) light that penetrates our atmosphere initiates various photochemical and photobiological processes. However, the absence of extremely short UV pulses has so far hindered our ability to fully capture the mechanisms at the very early stages of such processes. This is important because the concerted motion of electrons and nuclei in the first few femtoseconds often determines molecular reactivity. Here we investigate the dissociative dynamics of iodomethane following UV photoexcitation, utilizing mass spectrometry with a 5 fs time resolution. The short duration of the UV pump pulse (4.2 fs) allows the ultrafast dynamics to be investigated in the absence of any external field, from well before any significant vibrational displacement occurs until dissociation has taken place. The experimental results combined with semi-classical trajectory calculations provide the identification of the main dissociation channels and indirectly reveal the signature of a conical intersection in the time-dependent yield of the iodine ion. Furthermore, we demonstrate that the UV-induced breakage of the C-I bond can be prevented when the molecule is ionized by the probe pulse within 5 fs after the UV excitation, showcasing an ultrafast stabilization scheme against dissociation.

Clay mineral mediated dynamics of CO2 hydrate formation and dissociation: Experimental insights for carbon sequestration

Marine sediment-based CO2 sequestration through hydrate formation is a promising approach for long-term CO2 storage. Despite the prevalence of clay minerals in marine sediments, their impact on CO2 hydrate dynamics remains disputed and necessitates validation. This study systematically investigated the effect of clay minerals, specifically Ca-montmorillonite (Ca-mmt) and illite, on CO2 hydrates nucleation, growth, and dissociation in clay suspensions (0–10 wt% concentrations). Clay minerals significantly promoted CO2 hydrate nucleation by providng additional nucleation sites and influencing water distribution through the surface electric field. Ca-mmt exhibited a more pronounced nucleation effect due to stronger hydration ability of Ca2+ increasing nucleation sites and local CO2 concentration. Both clay minerals enhanced CO2 hydrate growth, with concentration-dependent effects that differ between clay types. Ca-mmt exhibited a higher growth rate at lower concentrations (≤1 wt%), but a lower rate at higher concentrations (>1 wt%) due to the stronger swelling and aggregation ability upon water contact. Morphological analysis revealed the clay minerals’ impact on fluid behavior and mass transfer during hydrate growth. During dissociation, clay minerals impeded the process, prolonging overall dynamics. This study highlights the impact of physicochemical disparities between Ca-mmt and illite on CO2 hydrate dynamics, underscoring the importance of these interactions for CO2 sequestration.

High-resolution anionic velocity map imaging apparatus for dissociative electron attachment dynamics study.

Dissociative electron attachment (DEA) of a molecular target XY, e- + XY → XY- → X + Y-, is an important process in plasma, atmosphere, interstellar space, and ionizing radiation. DEA dynamics, i.e., the formation and fragmentation of an electron-molecule resonant complex, can be unveiled by measuring the product Y- with the velocity map imaging (VMI) technique. However, it is still challenging to achieve a high-resolution VMI measurement. Recently, we developed a high-resolution DEA apparatus that combined the VMI technique with a trochoidal electron monochromator. The energy spread (around 500meV) of thermally emitted incident electrons can be reduced remarkably, but the monochromatized electrons become diffuse again in energy when being pulsed with an electric pulse applied on the grid electrode because the electron beam must be pulsed in the VMI measurement. Now this long-standing technical contradiction is settled by introducing a parallel resistance-capacitor circuit to the electrode of an electron gun. A delay-line detector is used for the VMI measurement, which allows the three-dimensional velocity or momentum images of multiple anionic yields to be recorded efficiently. Our high-resolution VMI apparatus works at a pulse frequency of 5kHz and an energy spread of about 120-150meV, and its credible performances are exhibited by the measurements of the DEA processes of CO(a3Π) and NO2.

Imaging study of O3 photodissociation in the Huggins band.

We report a velocity-mapped ion imaging study of the photodissociation of O3 in the Huggins band. The O(3PJ) images show evidence for three electronic channels producing O2(X3Σg-), O2(a1∆g), and O2(b1Σg+) state fragments, with the latter two arising from the spin-forbidden photodissociation of O3. Forward convolution simulations of the derived total translational energy distributions permit extraction of the vibrational state distribution for each O2 electronic state. All these distributions peak near v = 0 and decrease monotonically with the vibrational state. The wavelength-dependent branching of the three electronic channels has been determined and is approximately constant over the wavelength region studied (322-328nm). We have observed that the O2 electronic state branching ratios depend on the coincident O(3PJ) spin-orbit state, and the O2(b1Σg+) state is particularly sensitive. These results are qualitatively consistent with previous calculations on the coupling of the initially excited state to dissociative states by Rosenwaks and Grebenshchikov [J. Phys. Chem. A. 114, 9809-9819 (2010)]. The spatial anisotropy of the three dissociation channels has been determined through analysis of the O(3P0) angular distributions. The results are consistent with recent calculations but differ from previous experimental reports. The experimental results provide detailed information on the dissociation dynamics and should motivate new calculations.

Enhanced Intramolecular Hole Transfer in Block Copolymer Enables >15% and Operational Stable Single-Material-Organic Solar Cells.

Recent studies on narrow bandgap all-conjugated block copolymer (BCP) single-material-organic solar cells (SMOSCs) have made unprecedented progress in power conversion efficiency (PCE); however, it still lacks understanding of the structure-property relationship in these highly mixed materials. Herein, the impact of different synthetic protocols (direct synthesis (d-BCP) versus sequential synthesis (s-BCP)) is first investigated on the relevant photovoltaic properties. Targeting the same BCP, namely PBDB-T-b-PYIT, it is found that the change in polymerization reaction leads to quite different optical and transport properties. The d-BCP outputs a record-high PCE of 15.02% for SMOSCs as well as enhanced operation stability under simulated 1-sun illumination, which is significantly higher than that of s-BCP (10.33%) and even close to its bulk heterojunction (BHJ) counterparts. Detailed transient absorption spectroscopy reveals ultrafast dynamics of charge transfer (CT) and exciton dissociation in BCP. In together with morphology characterization, it is revealed that the d-BCP has more phase pure composition, enhanced molecular ordering, and higher intramolecular CT efficiency relative to those of s-BCP. These findings gain insight into both the structure and carrier dynamic of BCP and demonstrate the possibility of achieving high-efficiency and stable SMOSCs.

Calculations of Dissociation Dynamics of CH3OH on a Global Potential Energy Surface Reveal the Mechanism for the Formation of HCOH; Roaming Plays a Role.

The experimental observation of hydroxymethylene, HCOH, following excitation of methanol at 193 nm, was reported recently (Hockey, E. K.; McLane, N.; Martí, C.; Duckett, L.; Osborn, D. L.; Dodson, L. G. Direct Observation of Gas-Phase Hydroxymethylene: Photoionization and Kinetics Resulting from Methanol Photodissociation. J. Am. Chem. Soc. 2024, 146, 14416-14421, 10.1021/jacs.4c03090). This stimulated us to investigate a dynamic mechanism for its formation using a global potential energy surface for the ground electronic state (S0) of methanol. We show via quasi-classical trajectory calculations that hydroxymethylene is indeed formed under the reasonable assumption that the initially excited state undergoes rapid internal conversion to S0. From the trajectories, fractional yields of the six major product channels are determined as a function of excitation energy, and the rate of production of each is determined from the fractions and rate of methanol disappearance. Roaming is observed in trajectories leading to the OH and CH3 products as well as in those leading to CH2OH + H and non-reactive trajectories. A "frustrated" roaming accounts for roughly 20% of the HCOH production.

Molecular insights into methane hydrate dissociation: Role of methane nanobubble formation.

Understanding the underlying physics of natural gas hydrate dissociation is necessary for efficient CH4 extraction and in the exploration of potential additives in the chemical injection method. Silica being "sand" is already present inside the reservoir, making the silica nanoparticle a potential green additive. Here, molecular dynamics (MD) simulations have been performed to investigate the dissociation of the CH4 hydrate in the presence and absence of ∼1, ∼2, and ∼3nm diameter hydrophilic silica nanoparticles at 100bar and 310K. We find that the formation of a CH4 nanobubble has a strong influence on the dissociation rate. After the initial hydrate dissociation, the rate of dissociation slows down till the formation of a CH4 nanobubble. We find the critical concentration and size limit to form the CH4 nanobubble to be ∼0.04 molefraction of CH4 and ∼40 to 50 CH4 molecules, respectively. The solubility of CH4 and the chemical potential of H2O and CH4 are determined via Gibbs ensemble Monte Carlo simulations. The liquid phase chemical potential of both H2O and CH4 in the presence and absence of the nanoparticle is nearly the same, indicating that the effect of this additive will not be significant. While the formation of the hydration shell around the nanoparticle via hydrogen bonding confirms the strength of interactions between the water molecules and the nanoparticle in our MD simulations, the contact of the nanoparticle with the interface is infrequent, leading to no explicit effect of the nanoparticle on the dynamics of methane hydrate dissociation.

Dissoziative Elektronenanlagerungsdynamik eines vielversprechenden Krebsmedikaments zeigt sein Potential als Radiosensitizer

Abstract2‐Bromo‐1‐(3,3‐dinitroazetidin‐1‐yl)ethan‐1‐on (RRx‐001) ist ein Chemotherapeutikum für sauerstoffarme Tumore und zeigte bereits Synergieeffekte in Kombination mit Strahlentherapie. Die Wechselwirkung des Moleküls mit niederenergetischen Sekundärelektronen, die in großer Zahl in der physikalisch‐chemischen Phase der Bestrahlung gebildet werden, könnten für diesen Synergieeffekt verantwortlich sein. Die vorliegende Studie konzentriert sich auf die ersten Schritte in der Wechselwirkung von RRx‐001 mit niederenergetischen Elektronen, in denen das temporäre negative Ion gebildet wird und rasch fragmentiert. Die Kombination von Resultaten zweier Versuchsaufbauten erlaubt es uns, den Zerfall des RRx‐001 Anions auf verschiedenen Zeitskalen zu entflechten. Die alleinige Anwesenheit des eingefangenen Elektrons führt zu einer raschen Abspaltung von NO2 und HNO2, während NO2− und Br− Anionen direkt beziehungsweise über andere Zwischenprodukte gebildet werden. Auf Basis quantenchemischer Rechnungen schlagen wir einen bidirektionalen Wechsel zwischen π*(NO2) und σ*(C−Br) Zuständen vor, welcher die experimentellen Spektren erklärt. Die beobachtete schnelle Dynamik lässt auch Schlussfolgerungen für die Chemie des Anions in der kondensierten Phase zu.

Mean field approximation of a surface-reaction growth model with dissociation

We utilize mean field approximation to derive a set of coupled non-linear differential equations for a surface-reaction growth model, incorporating dissociative adsorption processes. These equations account for inaccessible sites caused by the height differences in the growing film, which inhibit dissociative adsorption. Numerical integration of these equations highlights the substantial effect of dissociation rates on growth kinetics, showing excellent agreement with prior kinetic Monte Carlo simulations, offering crucial insights into the interaction between dissociative adsorption and surface growth dynamics.

Potential energy of heavy quarkonium in flavor-dependent systems from a holographic model

Within the framework of the Einstein-Maxwell-dilaton model, which incorporates information on the equation of state and baryon number susceptibility from lattice results, we have conducted a comprehensive analysis of the potential energy, running coupling, and dissociation time for heavy-quark–antiquark pairs using gauge/gravity duality. This study encompasses various systems, including pure gluon systems, 2-flavor systems, 2+1-flavor systems, and 2+1+1-flavor systems under finite temperature and chemical potential. The results reveal that the linear component of the potential energy diminishes as the flavor increases. It is also found that our results are extremely close to the recent lattice results for 2+1-flavors at finite temperature. Moreover, we have thoroughly investigated the dissociation distance and effective running coupling constant of quark-antiquark pairs to gain a comprehensive understanding of their behavior across various flavors. Finally, we have examined real-time dynamics of quark dissociation. The findings indicate that the dissociation time of quark-antiquark pairs is dependent on temperature, chemical potential, and flavor of the systems. Published by the American Physical Society 2024

Tracking ultrafast non-adiabatic dissociation dynamics of the deuterated water dication molecule.

We applied reaction microscopy to elucidate fast non-adiabatic dissociation dynamics of deuterated water molecules after direct photo-double ionization at 61eV with synchrotron radiation. For the very rare D+ + O+ + D breakup channel, the particle momenta, angular, and energy distributions of electrons and ions, measured in coincidence, reveal distinct electronic dication states and their dissociation pathways via spin-orbit coupling and charge transfer at crossings and seams on the potential energy surfaces. Notably, we could distinguish between direct and fast sequential dissociation scenarios. For the latter case, our measurements reveal the geometry and orientation of the deuterated water molecule with respect to the polarization vector that leads to this rare 3-body molecular breakup channel. Aided by multi-reference configuration-interaction calculations, the dissociation dynamics could be traced on the relevant potential energy surfaces and particularly their crossings and seams. This approach also unraveled the ultrafast time scales governing these processes.

High-Energy Reaction Dynamics of N3.

The atom-exchange and atomization dissociation dynamics for the N(4S) + N2(1Σg+) reaction are studied using a reproducing kernel Hilbert space (RKHS)-based, global potential energy surface (PES) at the MRCI-F12/aug-cc-pVTZ-F12 level of theory (MRCI, multireference configuration interaction). For the atom exchange reaction (NANB + NC → NANC + NB), computed thermal rates and their temperature dependence from quasi-classical trajectory (QCT) simulations agree to within error bars with the available experiments. Companion QCT simulations using a recently published CASPT2-based PES confirm these findings. For the atomization reaction, leading to three N(4S) atoms, the computed rates from the RKHS-PES overestimate the experimentally reported rates by 1 order of magnitude, whereas those from the permutationally invariant polynomial (PIP)-PES agree favorably, and the T dependence of both computations is consistent with the experiment. These differences can be traced back to the different methods and basis sets used. The lifetime of the metastable N3 molecule is estimated to be ∼200 fs depending on the initial state of the reactants. Finally, neural-network-based exhaustive state-to-distribution models are presented using both PESs for the atom exchange reaction. These models will be instrumental for a broader exploration of the reaction dynamics of air.

Dissociative Electron Attachment Dynamics of a Promising Cancer Drug Indicates Its Radiosensitizing Potential.

2-Bromo-1-(3,3-dinitroazetidin-1-yl)ethan-1-one (RRx-001) is a hypoxic cell chemotherapeutics with already demonstrated synergism in combined chemo-radiation therapy. The interaction of the compound with secondary low-energy electrons formed in large amounts during the physico-chemical phase of the irradiation may lead to these synergistic effects. The present study focuses on the first step of RRx-001 interaction with low-energy electrons in which a transient anion is formed and fragmented. Combination of two experiments allows us to disentangle the decay of the RRx-001 anion on different timescales. Sole presence of the electron initiates rapid dissociation of NO2 and HNO2 neutrals while NO2 - and Br- anions are produced both directly and via intermediate complexes. Based on our quantum chemical calculations, we propose that bidirectional state switching between π*(NO2) and σ*(C-Br) states explains the experimental spectra. The fast dynamics monitored will impact the condensed phase chemistry of the anion as well.

Effects of stepwise depressurisation rate on methane hydrate dissociation dynamics at pore scale using microfluidic experiments

Methane hydrate, recognized as a potential alternative energy source, faces challenges in achieving efficient production. Stepwise depressurisation has emerged as a viable technique for enhancing productivity, yet optimizing the depressurisation rate remains a complex issue. This study employs pore-scale experiments using microfluidic chips to examine the dissociation characteristics of methane hydrate under varying stepwise depressurisation rates. At a high depressurisation rate of 0.4 MPa/15 min, the dissociation process exhibits a three-stage pattern: stabilisation, rapid dissociation, and slow dissociation. During these stages, the mass transfer limitation in the water phase significantly impedes the dissociation rate. The gas-water migration triggered by depressurisation can mitigate this limitation. As the depressurisation rate is reduced to 0.2 MPa/15 min, the rapid dissociation stage splits into two due to a decrease in gas-water migration intensity. The dissociation rate decreases by 45% compared to the 0.4 MPa/15 min case. This results from an insufficient driving force for dissociation, necessitating another depressurisation step. Further reduction of the depressurisation rate to 0.1 MPa/15 min leads to a less pronounced gas-water migration, which is inadequate to significantly counteract the mass transfer limitation. As a result, the rapid dissociation phase occurring at a depressurisation rate of 0.4 MPa/15 min, which exhibits an average dissociation rate of 0.2%/s, subsequently transitions into a more uniform and slower dissociation stage, where the average rate of dissociation declines to below 0.07%/s. The experimental results offer valuable insights for guiding hydrate exploration strategies during the stepwise depressurisation process by adjusting the depressurisation rate to regulate production.

Assessing the dynamics of O2 desorption from cobalt phthalocyanine by in situ electrochemical scanning tunneling microscopy

We report here the in situ electrochemical scanning tunneling microscopy (ECSTM) study of cobalt phthalocyanine (CoPc)-catalyzed O2 evolution reaction (OER) and the dynamics of CoPc-O2 dissociation. The self-assembled CoPc monolayer is fabricated on Au(111) substrate and resolved by ECSTM in 0.1 M KOH electrolyte. The OH− adsorption on CoPc prior to OER is observed in ECSTM images. During OER, the generated O2 adsorbed on CoPc is observed in the CoPc monolayer. Potential step experiment is employed to monitor the desorption of OER-generated O2 from CoPc, which results in the decreasing surface coverage of CoPc-O2 with time. The rate constant of O2 desorption is evaluated through data fitting. The insights into the dynamics of Co-O2 dissociation at the molecular level via in situ imaging help understand the role of Co-O2 in oxygen reduction reaction (ORR) and OER.

Investigating electron-induced dissociation dynamics in the organometallic precursor Fe(CO)5: a nonadiabatic molecular dynamics approach

This research employs excited states molecular dynamics simulations to explore the electron-induced dissociation behavior of Fe(CO)5 molecules, with the specific focus on electronic excitation. The study initiates with the detailed analysis of the molecule’s stable ground state structure. Subsequent simulations reveal distinctive dissociation patterns in various bonds, particularly noting the rapid dissociation of bonds between Fe and C1, Fe and C2, while those with Fe and C3 oscillate without complete dissociation. Emphasizing the influence of the transition from the highest occupied molecular orbital to the lowest unoccupied molecular orbital on reactivity, the investigation sheds light on the charge transfer phenomenon during dissociation through Bader analysis. Insights into transitions between excited and ground states are derived from the time evolution of the Kohn–Sham orbital. This study significantly contributes to understanding intricate dissociation mechanisms under electronic excitation, especially in molecules like Fe(CO)5 characterized by complex chemical bonds. Beyond theoretical exploration, the research holds practical significance for applications in nanomaterials, such as focused electron beam-induced deposition and the fabrication of nanoscale structures, enriching our comprehension of electronic-excitation-induced dissociation and advancing both theoretical understanding and practical applications in this field.

Dynamics of the Decomposition of Gas Molecules Containing Sulfur and Nitrogen from Char-S and Char-N Structures in Combustion and Pyrolysis Reactions

ABSTRACT Combustion states of char-S (C14H16O4S) and char-N (C18H19NO3) sub function molecules in a limited number of oxygen environments and pyrolysis states at high temperatures were examined quantum mechanically. In the study, the formation of all gases, with or without carbon, were determined. All the dynamics in which the O2 molecule could be effective in the combustion mechanism and all the elements that could affect the decomposition in the pyrolysis event were determined. The dynamics of the formation and disappearance of the highly stable CO molecule and CH2O (formaldehyde) molecules were shown in detail. It has been shown that the CO molecule is a catalysis that can bond with hydrocarbon groups and decompose them into small hydrocarbon groups at high temperature. In this study, it was shown that high temperature-dependent vibration and rotational energies, CO molecule and H-atom transfers play a role in the decomposition in the pyrolysis system, and the aromatic carbon ring group is the last particle group to decompose. In addition, the formation and dissociation dynamics of sulfoxylic acid, thioformic acid, hydrogen sulfide molecules originating from the Char-S system, as well as the formation conditions of hydrogen cyanide and pyridinyl molecules originating from the Char-N system, were determined. The study also showed that since the N-atom is located in the aromatic carbon ring, it makes the emergence of the nitrous oxide molecule difficult in pyrolysis systems.

Correlated electron-nuclear dynamics of photoinduced water dissociation on rutile TiO2.

Elucidating the mechanism of photoinduced water splitting on TiO2 is important for advancing the understanding of photocatalysis and the ability to control photocatalytic surface reactions. However, incomplete experimental information and complex coupled electron-nuclear motion make the microscopic understanding challenging. Here we analyse the atomic-scale pathways of photogenerated charge carrier transport and photoinduced water dissociation at the prototypical water-rutile TiO2(110) interface using first-principles dynamics simulations. Two distinct mechanisms are observed. Field-initiated electron migration leads to adsorbed water dissociation via proton transfer to a surface bridging oxygen. In the other pathway, adsorbed water dissociation occurs via proton donation to a second-layer water molecule coupled to photoexcited-hole transfer promoted by in-plane surface lattice distortions. Two stages of non-adiabatic in-plane lattice motion-expansion and recovery-are observed, which are closely associated with population changes in Ti3d orbitals. Controlling such highly correlated electron-nuclear dynamics may provide opportunities for boosting the performance of photocatalytic materials.