eV Collision Energy Research Articles

Imaging the Ion-Molecule Reaction Dynamics of O- + CD4.

While neutral reactions involved in methane oxidation have been intensively studied, much less information is known about the reaction dynamics of the oxygen radical anion with methane. Here, we study the scattering dynamics of this anion-molecule reaction using crossed-beam velocity map imaging with deuterated methane. Differential scattering cross sections for the deuterium abstraction channel have been determined at relative collision energies between 0.2 and 1.5 eV and ab initio calculations of the important stationary points along the reaction pathway have been performed. At lower collision energies, direct backscattering and indirect complex-mediated reaction dynamics are observed, whereas at higher energies, sideways deuterium stripping dominates the reaction. Above 0.7 eV collision energy, a suppressed cross section is observed at low product ion velocities, which is likely caused by the endoergic pathway of combined deuteron/deuterium transfer, forming heavy water. The measured product internal energy is attributed mainly to the low-lying deformation and out-of-plane bending vibrations of the methyl radical product. The results are compared with a previous crossed-beam result for the reaction of oxygen anions with nondeuterated ̧methane and with the related neutral-neutral reactions, showing similar dynamics and qualitative agreement.

Beyond vanilla: The dissociation mechanism of vanillin in four charge states

We compare the unimolecular decay mechanism of vanillin in four charge states. The unimolecular thermal decomposition of the neutral and dissociative ionization reactions in the cation have already been addressed in synchrotron-based photoionization studies. The picture is completed here by studying the collision-induced dissociation mechanism of protonated vanillin cations and deprotonated vanillin anions in the 5–30 eV collision energy range. The mass spectrometric observations are rationalized by ab initio calculations, which reveal the mechanism and the energetics of dissociation pathways. In the positive ion mode, the aldehyde oxygen is protonated, after which CO is lost. In contrast to previous results, CO loss is found to be the sole primary fragmentation pathway of protonated vanillin. Two hydrogen migration steps to the benzene ring open sequential CH3OH and CH3 loss channels to yield C6H5O+ and C6H6O2+, respectively. The former fragment ion can continue to lose CO, associated with ring contraction and producing the cyclopentadiene cation, C5H5+. In the negative ion mode, the proton is removed from the hydroxyl group. The primary dissociation channel of deprotonated vanillin corresponds to (C)OCH3 bond breaking in the methoxy group to form C7H4O3− at m/z 136. This species goes on to produce C6H4O2− and C6H4O− anions via CO and CO2 loss, respectively, in sequential dissociation processes at higher collision energies. We compare the protonated and deprotonated vanillin fragmentation pathways with those observed in the decomposition of neutral vanillin and with the dissociation pathways of the vanillin cation. The initial decomposition step for neutral, cationic, and deprotonated vanillin is methyl loss by direct CO bond breaking, often followed by loss of CO. In contrast, protonated vanillin first loses CO after isomerization.

An improved model for predicting the erosion within the DEM framework

For investigating the erosion caused by particle impact, an erosion model based on the particle impact energy has been proposed in our previous study, which can be called IEEM (Impact Energy Erosion Model). By incorporating IEEM with DEM (Discrete Element Method), the erosion caused by particle impact can be numerically predicted. However, IEEM assumes that all particle impacts lead to erosion, which contradicts the reality where gentle particle impacts with low collision energy do not cause erosion. Therefore, an improved erosion model called FIEEM (Filtering Impact Energy Erosion Model) is devised by introducing the concept of filtration into IEEM. In FIEEM, the low-energy particle collisions are filtered by comparing the contact stress with the flow stress of the target material so that these collisions cannot cause erosion, and the Hertz contact theory is employed to determine the accurate contact stress. Subsequently, the DEM simulations of the charge behaviors and liner wear in an industrial-scale SAG (Semi-Automatic Grinding) mill are conducted and then compared with the experimental data for validating the accuracy and effectiveness of FIEEM. Additionally, the discussion regarding the difference of the predicted erosion between IEEM and FIEEM is also presented from the point of effective collision energy.

Globally Accurate Gaussian Process Potential Energy Surface and Quantum Dynamics Studies on the Li(2S) + Na2 → LiNa + Na Reaction at Low Collision Energies.

The LiNa2 reactive system has recently received great attention in the experimental study of ultracold chemical reactions, but the corresponding theoretical calculations have not been carried out. Here, we report the first globally accurate ground-state LiNa2 potential energy surface (PES) using a Gaussian process model based on only 1776 actively selected high-level ab initio training points. The constructed PES had high precision and strong generalization capability. On the new PES, the quantum dynamics calculations on the Li(2S) + Na2(v = 0, j = 0) → LiNa + Na reaction were carried out in the 0.001-0.01 eV collision energy range using an improved time-dependent wave packet method. The calculated results indicate that this reaction is dominated by a complex-forming mechanism at low collision energies. The presented dynamics data provide guidance for experimental research, and the newly constructed PES could be further used for ultracold reaction dynamics calculations on this reactive system.

Direct dissociative recombination of HCO+via the core-excited doublet and the lowest quartet states.

The dissociative recombination of HCO+ up to 1 eV collision energy is studied. New calculations for several core-excited HCO states provide improved potential energy surfaces crossing the HCO+ ground state surface in the vicinity of its equilibrium geometry. Wave packet analysis leads to significantly higher contributions of the direct mechanism to the cross section for electron energy ε < 0.7 eV than according to earlier studies [Larson et al., Phys. Rev. A, 2012, 85, 042702]. The limit H + CO(a3Π) is found to be the most probable exit channel. We discuss the improved agreement of theory with the latest experiments [Hamberg et al., J. Phys. Chem., 2014, 118, 6034] resulting from combination with the most recent calculations of the indirect process [Fonseca dos Santos et al., J. Chem. Phys., 2014, 140, 164308]. For the lowest quartet surfaces some vibrational states and their population and depopulation (mediated by spin-orbit coupling) are examined.

A statistical investigation of the rate constants for the H+ + HD reaction at temperatures of astrophysical interest.

The H+ + HD(v, j) reaction has been investigated in detail by means of a statistical quantum method. State-to-state cross sections and rate constants for transitions between reactants and rovibrational states HD(v', j') of the product arrangement with energies below 0.9eV collision energy [that is, HD(v = 0, j = 0-11) and HD(v = 1, j = 0-6)] have been calculated. For the other product channel, D+ + H2(v', j'), rovibrational states up to (v' = 0, j' = 9) have been considered for the calculation of the corresponding thermal rate. Present predictions are compared with previously reported theoretical and experimental rates. Finally, cooling functions for HD due to proton and atomic hydrogen collisions are computed in the low-density regime. We find that the much larger HD-H+ cooling function, as compared with that of HD-H, does not compensate for the low H+/H abundance ratio in astrophysical media so that HD cooling is dominated by HD-H (or HD-H2) collisions.

Final-state-resolved mutual neutralization in I+ - I− collisions

We have studied the mutual neutralization reaction of atomic iodine ions (i.e., ${\mathrm{I}}^{+}+{\mathrm{I}}^{\ensuremath{-}}\ensuremath{\rightarrow}\text{I}+\text{I}$) in a cryogenic double electrostatic ion-beam storage-ring apparatus. Our results show that the reaction forms iodine atoms either in the ground-state configuration ($\mathrm{I}(5{p}^{5}\phantom{\rule{0.16em}{0ex}}{}^{2}{P}^{\ensuremath{\circ}})$, \ensuremath{\sim}40%) or with one atom in an electronically excited state ($\mathrm{I}(6s{\phantom{\rule{0.16em}{0ex}}}^{2}[2]$), $\ensuremath{\sim}60%$), with no significant variation over the branching ratios in the studied collision-energy range (0.1--0.8 eV). We estimate the total charge-transfer cross section to be of the order of ${10}^{\ensuremath{-}13}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{2}$ at 0.1 eV collision energy. Ab initio relativistic electronic structure calculations of the potential-energy curves of ${\mathrm{I}}_{2}$ suggest that the reaction takes place at short internuclear distances. The results are discussed in view of their importance for applications in electric thrusters.

The influence of collision energy on magnetically tuned 6Li-6Li Feshbach resonance

The effect of collision energy on the magnetically tuned 6Li–6Li Feshbach resonance (FR) is investigated theoretically by using the coupled-channel (CC) method for the collision energy ranging from 1 μK ⋅ k B to 100 μK ⋅ k B. At the collision energy of 1 μK ⋅ k B, the resonance positions calculated are 543.152 Gs (s wave, the unit 1 Gs = 10−4 T), 185.109 Gs (p wave |ml | = 0), and 185.113 Gs (p wave |ml | = 1), respectively. The p-wave FR near 185 Gs exibits a doublet structure of 4 mGs, associated with dipole–dipole interaction. With the increase of the collision energy, it is found that the splitting width remains the same (4 mGs), and that the resonance positions of s and p waves are shifted to higher magnetic fields with the increase of collision energy. The variations of the other quantities including the resonance width and the amplitude of the total scattering section are also discussed in detail. The thermally averaged elastic rate coefficients at T = 10, 15, 20, 25 K are calculated and compared.

Sudden increase in the degrees of freedom in dense QCD matter

In this paper, we analyzed charged particle transverse momentum spectra in high multiplicity events in proton–proton and nucleus–nucleus collisions at LHC energies from the ALICE experiment using the color string percolation model (CSPM). The color reduction factor and associated string density parameters are extracted for various multiplicity classes in [Formula: see text] collisions and centrality classes for heavy-ion collisions at various LHC energies to study the effect of collision geometry and collision energy. These parameters are used to extract the thermodynamical quantities temperature and the energy density of the hot nuclear matter. A universal scaling is observed in initial temperature when studied as a function of charged particle multiplicity scaled by transverse overlap area. From the measured initial energy density [Formula: see text] and the initial temperature T, a dimensionless quantity [Formula: see text] is constructed which is used to obtain the degrees of freedom (DOF) of the deconfined phase. A two-step behavior and a sudden increase in DOF of [Formula: see text]47 for the ideal gas, above the hadronization temperature (T [Formula: see text] 210[Formula: see text]MeV), are observed in case of heavy-ion collisions at LHC energies.

Theoretical Study of the Energy Disposal Mechanism and the State-Resolved Quantum Dynamics of the H + LiH+ → H2 + Li+ Reaction.

Despite several studies in the literature, the detailed quantum state-to-state level mechanism of the astrophysically important exoergic barrierless H + LiH+ → H2 + Li+ reaction is yet to be understood. In this work, we have investigated the energy disposal mechanism of the reaction in terms of integral reaction cross section, product internal state distributions, differential cross section, and rate constant. Fully converged and Coriolis coupled quantum mechanical calculations based on a time-dependent wave packet method have been performed at the state-to-state level on the ab initio electronic ground state potential energy surface (PES) constructed by Martinazzo et al. (J. Chem. Phys. 2003, 119, 11241-11248). The agreement between the present quantum mechanical and previous quasi-classical results is found even at very low relative translational energies of reagents. A non-statistical inverse Boltzmann vibrational distribution for the product is found. This is attributed to the "attractive" nature of the underlying PES, which facilitates the excess energy release mostly as product vibration (60-80%). The energy disposal in products is found to be unaffected by the rovibrational excitation of the reagent diatom due to the weak coupling between the vibrational modes of the reagent and the product. The mild effect of collision energy on the product energy disposal is ascribed to the effective coupling between the translational modes of the reagent and the product. It is found that the collisions lead to the formation of the product H2 in its rovibrationally excited levels.

Suppression of low product kinetic energies in reactions of FHO− and Cl−(H2O) with CH3I

Substantially different reaction dynamics, product branching ratios and time scales have been reported in crossed beam imaging experiments on the nucleophilic substitution reactions of Cl−(H2O) and F−(H2O) with CH3I at 0.3 eV collision energy [Bastian et al., J. Phys. Chem. A 124, 1929 (2020)]. In particular, it was speculated that Cl−(H2O) only undergoes nucleophilic substitution via a ligand exchange intermediate. Here, we present crossed-beam scattering results for the two title reactions that both show a suppression of low product kinetic energies. We discuss this mechanism in comparison with recent results on the ligand exchange in F−(H2O) + CH3I collisions. This also allows for a more detailed picture of the dynamics of hydrated nucleophilic substitution reactions at low collision energy.

Untargeted Screening of EPA/DHA Structured Phospholipids in Krill Oil by Chain-Lock-Driven Hydrophilic Interaction Liquid Chromatography Tandem Mass Spectrometry.

Eicosapentaenoic and docosahexaenoic acids structured phospholipids (PLEPA/DHA) have multiple biochemical and pharmacological effects on human health. In this study, EPA and DHA chains were locked under precursor ion scan (PreIS) mode for untargeted screening PLEPA/DHA in krill oil using hydrophilic interaction liquid chromatography tandem mass spectrometry (HILIC-MS/MS). The effect of collision energy and declustering potential on the fragmentation of EPA (m/z 301.2) and DHA (m/z 327.2) chains was studied. A total of 33 PLEPA/DHA were characterized (sn-1/sn-2) and quantified using regression models, including 16 PCEPA/DHA, 11 PEEPA/DHA, and 6 PIEPA/DHA. Afterward, this method was validated in terms of linearity (≥0.9978), sensitivity (LOD ≤ 4.02 μg·L-1), precision (RSDintraday ≤ 4.71%), and recovery (≥78.9%). Finally, the performance of HILIC-PreIS-MS/MS was compared with those of conventional methods, and the results indicated its superiority in selective screening PLEPA/DHA in krill oil.

Charge transfer dynamics in Ar+ + CO

Differential cross sections for the charge transfer reaction between Ar+ and CO have been measured using three-dimensional velocity map imaging in a crossed beam setup at the two relative collision energies 0.55 and 0.74 eV. We find dominant forward scattering with CO+ product ions predominantly in the vibrational levels =6,7 of the electronic ground state X. This is indicative of a direct resonant mechanism for the two argon spin-orbit states. At both collision energies also an isotropic distribution with product ions exhibiting high internal excitation is observed. This is more pronounced at the higher collision energy, where the first electronically excited state A becomes accessible. We conclude that the A-state is partially populated by the product ions at 0.74 eV collision energy and suggest that the isotropic distribution stems from the formation of a charge-transfer complex, in concurrence with previously performed studies.

State-selected ion-molecule reactions with VUV synchrotron radiation : the O2 + + C3H6 case

SynopsisO2 + molecular ion is produced by photoionization close to threshold at SOLEIL, DESIRS beam line. By means of coincidence methods, ions are prepared in selected vibrational and electronic states (X, v=0,3,15 and a, v=3). Their reactivity with the propene in single collision regime is studied in the guided ion beam in-strument CERISES, adding ability to vary the collision energy. Absolute reaction cross section and branching ratio are recorded for the 5 most intense reactive channels, described as dissociative charge transfer. Contrasted effects of internal and collision energy are observed.

Electron-Induced Excitation, Recombination, and Dissociation of Molecular Ions Initiating the Formation of Complex Organic Molecules

We review the study of dissociative recombination and ro-vibrational excitation of diatomic and small polyatomic molecular ions initiating complex organic molecules formation. In particular, we show how Multichannel Quantum Defect Theory (MQDT) and R-matrix methods are used to compute cross sections and rate coefficients for cations in well defined ro-vibrational levels of the ground electronic state, from sub-meV up to few eV collision energies. The most recent MQDT results are compared with either other theoretical data, or with measured data obtained in storage-ring experiments.

Effect of collision energy on plastic deformation under repeated impacts

Metal materials were found to undergo substantial cumulative plastic deformation while operating under ultra-low stress, repeated-impact conditions that were far below the yield points of the materials. Plastic deformation was not only related to stress, but also to the collision energy input. Low-energy, repeated-impact tests were carried out on YT01 and 65Mn samples using a fatigue testing machine fabricated in-house. A grid method with coordinates, scanning electron microscopy, and single-crystal x-ray diffraction were employed to study the effect of the collision energy on the cumulative deformation, layer strains, and microstructures of the materials. The following results were obtained. For impact-induced stresses with the same peak value, a greater cumulative deformation and higher layer strain were observed for larger collision energy inputs. The collision energy tended to have a more significant influence on deformation at locations closer to the surface. For the same collision energy, a greater cumulative deformation occurred as a result of the higher peak impact stress. The location at which the deformation terminated was related to the peak impact stress but unrelated to the collision energy. Analysis also revealed that as the collision energy increased, the sub-grains in the microstructure of the materials decreased in size, while the micro-strain increased. In conclusion, the collision energy was an important factor affecting the cumulative plastic deformation in repeated-impact collisions.

The Intricate Dynamics of the Si(3P) + OH(X2Π) Reaction.

The dynamics of the Si(3P) + OH(X2Π) → SiO(X1Σ+,v',j') + H(2S) reaction is investigated by means of the quasi-classical trajectory method on the electronic ground state X2A' potential energy surface in the 10-2-1 eV collision energy range. Although the reaction involves the formation of a long-lived intermediate complex, a high probability for back-dissociation to the reactants is found because of inefficient intravibrational redistribution of energy among the complex modes. At low collision energies, the reactive events are governed by a dynamics with mixed direct/indirect features. As the collision energy increases, the intermediate complex lifetime increases and final state distributions are found to be in reasonable agreement with statistical predictions obtained using the mean potential phase space theory, thus highlighting the indirect character of the process. These rich and puzzling dynamical features are in line with what has been previously observed for the S(3P) + OH(X2Π) reaction.

The effect of collision energy on the stereodynamics of the reaction triatomic NH2 system

The stereodynamics of the reaction H(2S) + NH (v = 0, 1, 2, 3; j = 0) → N(4S) + H2 are studied using the quasi-classical trajectory method on a double many-body expansion potential energy surface to understand the alignment and orientation of the product molecules in the collision energy range of 2–20 kcal·mol−1. The vibrational–rotational quantum number of the NH molecules is specifically investigated for v = 0, 1, 2, and 3 and j = 0. The differential cross section [DCS; ], and average rotational alignment factor are calculated. The stereodynamics results indicate that the reagent vibrational quantum number and initial collision energy significantly affect the distributions of the k–j′, k–k′–j′ and k–k′ vector correlations along with In addition, while DCS is extremely sensitive to the collision energy, it is not significantly affected by the vibrational excitation of the reagents.

Dynamics of dissociative chemisorption of O2 on Cu(100) surface: A theoretical study

The dynamics of O2 dissociative chemisorption on Cu(100) is studied by means of quasi-classical dynamics simulation making use of a 6-dimensional potential energy surface based on density functional theory (DFT) calculations. The sticking probability is found in reasonable agreement with experiment above 0.3 eV collision energy. However, theory fails at capturing the activated behaviour experimentally evidenced for lower energies. While molecular beam experiments exhibit an energetic threshold in the sticking curve, simulations show a high dissociation probability at collision energies below this threshold. Present calculations suggest that this discrepancy is due to dynamics governed by a direct dissociation mechanism steming from several barrierless reaction paths associated with an indirect dissociation mechanism governed by dynamic trapping. These direct and indirect components are strongly related to the structure of the PES questioning the reliability of the DFT calculations and the choice of the functional used. Beyond the question of the DFT accuracy, this theoretical work addresses the still open question of experiments/theory comparison for systems involving O2 and metal surfaces such as Cu(100).

Dynamics of proton transfer from ArH+ to CO

The reaction of ArH+ with CO is a fast proton transfer reaction that can form two different isomers, HCO+ and HOC+. It has been investigated in a crossed beam experiment and with direct dynamics simulations at collision energies ranging from 0.4 to 2.4 eV. Images of the differential cross sections reveal dominant forward scattering, which is evidence for direct dynamics. The measured product internal energies are primarily determined by the reaction enthalpy and only at large scattering angles depend noticeably on the collision energy. The computational results agree well with the measured internal energy and scattering angle distributions and with the previously measured total rate constant. The direct reaction dynamics with dominant forward scattering are well reproduced by the almost step like opacity functions. The HCO+/HOC+ branching is found to be close to 2:1 in the simulations at 0.83 eV and 2.37 eV collision energy. A mode-specific vibrational analysis provides further insight into the isomer specific distribution of the product internal excitation.