Inelastic scattering of H atoms from surfaces

We have developed an instrument that uses photolysis of hydrogen halides to produce nearly monoenergetic hydrogen atom beams and Rydberg atom tagging to obtain accurate angle-resolved time-of-flight distributions of atoms scattered from surfaces. The surfaces are prepared under strict ultrahigh vacuum conditions. Data from these experiments can provide excellent benchmarks for theory, from which it is possible to obtain an atomic scale understanding of the underlying dynamical processes governing H atom adsorption. In this way, the mechanism of adsorption on metals is revealed, showing a penetration–resurfacing mechanism that relies on electronic excitation of the metal by the H atom to succeed. Contrasting this, when H atoms collide at graphene surfaces, the dynamics of bond formation involving at least four carbon atoms govern adsorption. Future perspectives of H atom scattering from surfaces are also outlined

Effective medium theory for bcc metals: Electronically non-adiabatic H atom scattering in full dimensions

In summary, we have extended the EMT formalism derived for fcc metals22 to the bcc case. We then fit the newly derived formulae to DFT data for H interacting with W and Mo, which led to full dimensional PESs and electron densities. We employed the PESs and the electron densities to carry out electronically non-adiabatic MD simulations of H atom scatter- ing, following previous work that used the LDFA approximation with a Langevin propagator. Specifically, we predict energy loss distributions for H scattering from (111) and (110) facets of these two metals at 2.76 eV incidence energy. Although no experiments are currently available for bcc metals, our results are similar to what has been seen for H scattering from fcc metals. This suggests that the current results are likely to be a reliable prediction of experiment. We find only subtle differ- ences in the energy loss distributions arising from the scatter- ing of H atom with these two metals; however, scattering from the (111) and (110) facets are distinctly different. Remarkably, on the (110) facet, we predict a clearly resolvable energy loss peak that arises from sub-surface scattering. The calculations Fig. 9 Distribution of specular scattering events as a function of the energy loss and the depth of penetration of H atom scattered from (a) Mo(110), (b) Mo(111), (c) W(110), and (d) W(111). The surface temperature is 70 K. The other conditions are the same as in Fig. 8. The signal above the black, dashed line indicate from which layer the projectiles repelled. The labels top, hcp and fcc refer to the high-symmetry sites of the (111) facet and are shown in Fig. 1(b). The bin sizes are 0.027 eV and 0.063 Å. Table 3 Sticking coefficient S0 computed from the same set of trajec- tories that were used for the calculation of the specular energy loss distributions shown in Fig. 8 System 300 K 70 K H/Mo(110) 0.44 0.44 H/Mo(111) 0.40 0.41 H/W(110) 0.42 0.41 H/W(111) 0.40 0.40 Paper PCCPOpen Access Article. Published on 04 April 2022. Downloaded on 6/8/2022 3:06:58 PM.This article is licensed under aCreative Commons Attribution 3.0 Unported Licence.View Article Online 8746 | Phys. Chem. Chem. Phys., 2022, 24, 8738–8748 This journal is © the Owner Societies 2022predict that the subsurface scattering is most easily seen for H scattering from W(110) at reduced surface temperatures

Revealing Willingness of Consumers to the Information Economy

The current economic conditions, together with the highly developed information and communication technologies, provide business entities with a variety of opportunities to work with consumers. The article relates the experience in revealing the level of readiness of educational services consumers – students – to a meaningful and productive interaction with a higher education institution in an information economy. The author proposes a way of estimating such willingness and the aspiration to an independent search and analysis of information, basing on the results of the consumers’ questioning. Visualization of data, splitting the respondents into groups were applied in the study, as well as tools of the geometric mean and the Mann–Whitney U non-parametric statistical hypothesis test were used.Keywords: willingness to consume, information economy, management, competitive advantages.Vartotojų pasirengimo informacinei ekonomikai atskleidimasVolha KandratsenkaSantraukaŠiuolaikinės ekonomikos sąlygos kartu su aukštu komunikacijos ir informacijos technologijų lygiu suteikia verslo subjektams įvairių darbo su vartotojais galimybių. Straipsnyje apibrėžtas švietimo paslaugų vartotojų – studentų – pasirengimo lygis prasmingai ir efektyviai sąveikauti su aukščiausią išsilavinimą teikiančia institucija informacinės ekonomikos sąlygomis. Autorė pateikia tokio pasirengimo vertinimo būdą, taip pat identifikuoja siekį savarankiškai ieškoti ir analizuoti informaciją, atsižvelgiant į poreikių anketavimo rezultatus. Tyrimui buvo taikoma duomenų vizualizacija, respondentų grupavimas, panaudotas geometrinio vidurkio instrumentas ir neparametrinis statistinis Mann–Whitney U kriterijus

Multibounce and subsurface scattering of H atoms colliding with a van der Waals solid

We report the results of inelastic differential scattering experiments and full-dimensional molecular dynamics trajectory simulations for 2.76 eV H atoms colliding at a surface of solid xenon. The interaction potential is based on an effective medium theory (EMT) fit to density functional theory (DFT) energies. The translational energy-loss distributions derived from experiment and theory are in excellent agreement. By analyzing trajectories, we find that only a minority of the scattering results from simple single-bounce dynamics. The majority comes from multibounce collisions including subsurface scattering where the H atoms penetrate below the first layer of Xe atoms and subsequently re-emerge to the gas phase. This behavior leads to observable energy-losses as large as 0.5 eV, much larger than a prediction of the binary collision model (0.082 eV), which is often used to estimate the highest possible energy-loss in direct inelastic surface scattering. The sticking probability computed with the EMT-PES (0.15) is dramatically reduced (5 × 10–6) if we employ a full-dimensional potential energy surface (PES) based on Lennard-Jones (LJ) pairwise interactions. Although the LJ-PES accurately describes the interactions near the H–Xe and Xe–Xe energy minima, it drastically overestimates the effective size of the Xe atom seen by the colliding H atom at incidence energies above about 0.1 eV

Toward detection of electron-hole pair excitation in H-atom collisions with Au(111): Adiabatic molecular dynamics with a semi-empirical full-dimensional potential energy surface.

We report an analytic potential energy surface (PES) based on several hundred DFT energies for H interacting with a Au(111) surface. Effective medium theory is used to fit the DFT data, which were obtained for the Au atoms held at their equilibrium positions. This procedure also provides an adequate treatment of the PES for displacements of Au atoms that occur during scattering of H atoms. The fitted PES is compared to DFT energies obtained from ab initio molecular dynamics trajectories. We present molecular dynamics simulations of energy and angle resolved scattering probabilities at five incidence angles at an incidence energy, Ei = 5 eV, and at a surface temperature, TS = 10 K. Simple single bounce trajectories are important at all incidence conditions explored here. Double bounce events also make up a significant fraction of the scattering. A qualitative analysis of the double-bounce events reveals that most occur as collisions of an H-atom with two neighboring surface gold atoms. The energy losses observed are consistent with a simple binary collision model, transferring typically less than 150 meV to the solid per bounce

An axis-specific rotational rainbow in the direct scatter of formaldehyde from Au(111) and its influence on trapping probability.

The conversion of translational to rotational motion often plays a major role in the trapping of small molecules at surfaces, a crucial first step for a wide variety chemical processes that occur at gas-surface interfaces. However, to date most quantum-state resolved surface scattering experiments have been performed on diatomic molecules, and little detailed information is available about how the structure of nonlinear polyatomic molecules influences the mechanisms for energy exchange with surfaces. In the current work, we employ a new rotationally resolved 1 + 1' resonance-enhanced multiphoton ionization (REMPI) scheme to measure the rotational distribution in formaldehyde molecules directly scattered from the Au(111) surface at incidence kinetic energies in the range 0.3-1.2 eV. The results indicate a pronounced propensity to excite a-axis rotation (twirling) rather than b- or c-axis rotation (tumbling or cartwheeling), and are consistent with a rotational rainbow scattering model. Classical trajectory calculations suggest that the effect arises-to zeroth order-from the three-dimensional shape of the molecule (steric effects). Analysis suggests that the high degree of rotational excitation has a substantial influence on the trapping probability of formaldehyde at incidence translational energies above 0.5 eV

An experimentally validated neural-network potential energy surface for H atoms on free-standing graphene in full dimensionality

We present a first principles-quality potential energy surface (PES) describing the inter-atomic forces for hydrogen atoms interacting with free-standing graphene. The PES is a high-dimensional neural network potential that has been parameterized to 75945 data points computed with density-functional theory employing the PBE-D2 functional. Improving over a previously published PES (Jiang et al., Science, 2019, 364, 379), this neural network exhibits a realistic physisorption well and achieves a 10-fold reduction in the RMS fitting error, which is 0.6 meV/atom. We used this PES to calculate about 1.5 million classical trajectories with carefully selected initial conditions to allow for direct comparison to results of H- and D-atom scattering experiments performed at incidence translational energy of 1.9 eV and a surface temperature of 300 K. The theoretically predicted scattering angular and energy loss distributions are in good agreement with experiment, despite the fact that the experiments employed graphene grown on Pt(111). The remaining discrepancies between experiment and theory are likely due to the influence of the Pt substrate only present in the experiment.Comment: submitted to PCCP, 8 figures, reference arXiv:2007.03372 adde

Condensed-phase isomerization through tunnelling gateways

Quantum mechanical tunnelling describes transmission of matter waves through a barrier with height larger than the energy of the wave. Tunnelling becomes important when the de Broglie wavelength of the particle exceeds the barrier thickness; because wavelength increases with decreasing mass, lighter particles tunnel more efficiently than heavier ones. However, there exist examples in condensed-phase chemistry where increasing mass leads to increased tunnelling rates. In contrast to the textbook approach, which considers transitions between continuum states, condensed-phase reactions involve transitions between bound states of reactants and products. Here this conceptual distinction is highlighted by experimental measurements of isotopologue-specific tunnelling rates for CO rotational isomerization at an NaCl surface, showing nonmonotonic mass dependence. A quantum rate theory of isomerization is developed wherein transitions between sub-barrier reactant and product states occur through interaction with the environment. Tunnelling is fastest for specific pairs of states (gateways), the quantum mechanical details of which lead to enhanced cross-barrier coupling; the energies of these gateways arise nonsystematically, giving an erratic mass dependence. Gateways also accelerate ground-state isomerization, acting as leaky holes through the reaction barrier. This simple model provides a way to account for tunnelling in condensed-phase chemistry, and indicates that heavy-atom tunnelling may be more important than typically assumed

H atom scattering from W(110): A benchmark for molecular dynamics with electronic friction.

Molecular dynamics with electronic friction (MDEF) at the level of the local density friction approximation (LDFA) has been applied to describe electronically non-adiabatic energy transfer accompanying H atom collisions with many solid metal surfaces. When implemented with full dimensional potential energy and electron density functions, excellent agreement with experiment is found. Here, we compare the performance of a reduced dimensional MDEF approach involving a simplified description of H atom coupling to phonons to that of full dimensional MDEF calculations known to yield accurate results. Both approaches give remarkably similar results for H atom energy loss distributions with a 300 K W(110) surface. At low surface temperature differences are seen; but, quantities like average energy loss are still accurately reproduced. Both models predict similar conditions under which H atoms that have penetrated into the subsurface regions could be observed in scattering experiments.The authors acknowledge the support of the French Embassy in Cuba, the University of Bordeaux, the CNRS, the Erasmus Mundus programme for funding and ISM and University of Bordeaux for providing computing resources. This work was conducted in the scope of the transborder joint Laboratory QuantumChemPhys: Theoretical Chemistry and Physics at the Quantum Scale (ANR-10-IDEX-03-02). This work was partly performed in the framework of the Elementary Dynamical Processes at Model Catalytic Surfaces (EDPMCS) Experiment, a part of the Molecular Physics at Interfaces Initiative at the Dalian Coherent Light Source. NH, AK and AMW acknowledge support for this project from the Max Planck Society Central Funds, the international partnership program of the Chinese Academy of Science (No. 121421KYSB20170012) as well as the Max Planck Institute for Multidisciplinary Sciences and the Georg-August University of Goettingen. We further acknowledge support from the Deutsche Forschungsgemeinschaft under Grant number 217133147, which is part of the Collaborative research Center 1073 operating Project A04. AK acknowledges European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 833404). OG acknowledges financial support by the Spanish Ministerio de Ciencia e Innovacion [Grant No. PID2019-107396GB-I00/AEI/10.13039/501100011033]