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The interaction of molecules, especially hydrocarbons, at the gas/ionic liquid (IL) surface plays a crucial role in supported IL catalysis. The dynamics of this process is investigated by measuring the trapping probabilities of n‐butane, iso‐butane and 1‐butene on a set of frozen 1‐alkyl‐3‐methylimidazolium‐based ILs [CnC1Im]X, where n=4, 8 and X−=Cl−, Br−, [PF6]− and [Tf2N]−. The decrease of the initial trapping probability with increasing surface temperature is used to determine the desorption energy of the hydrocarbons at the IL surfaces. It increases with increasing alkyl chain length n and decreasing anion size for the ILs studied. We attribute these effects to different degrees of alkyl chain surface enrichment, while interactions between the adsorbate and the anion do not play a significant role. The adsorption energy also depends on the adsorbing molecule: It decreases in the order n‐butane>1‐butene>iso‐butane, which can be explained by different dispersion interactions. [ABSTRACT FROM AUTHOR]

The impact of a reactant from the gas phase on the surface of a liquid and its transfer through this gas/liquid interface are crucial for various concepts applying ionic liquids (ILs) in catalysis. We investigated the first step of the adsorption dynamics of n‐butane on a series of 1‐alkyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide ILs ([CnC1Im][Tf2N]; n=1, 2, 3, 8). Using a supersonic molecular beam in ultra‐high vacuum, the trapping of n‐butane on the frozen ILs was determined as a function of surface temperature, between 90 and 125 K. On the C8‐ and C3‐ILs, n‐butane adsorbs at 90 K with an initial trapping probability of ≈0.89. The adsorption energy increases with increasing length of the IL alkyl chain, whereas the ionic headgroups seem to interact only weakly with n‐butane. The absence of adsorption on the C1‐ and C2‐ILs is attributed to a too short residence time on the IL surface to form nuclei for condensation even at 90 K. [ABSTRACT FROM AUTHOR]

Conversion of energy at the gas–solid interface lies at the heart of many industrial applications such as heterogeneous catalysis. Dissipation of parts of this energy into the substrate bulk drives the thermalization of surface species, but also constitutes a potentially unwanted loss channel. At present, little is known about the underlying microscopic dissipation mechanisms and their (relative) efficiency. At metal surfaces, prominent such mechanisms are the generation of substrate phonons and the electronically non-adiabatic excitation of electron–hole pairs. In recent years, dedicated surface science experiments at defined single-crystal surfaces and predictive-quality first-principles simulations have increasingly been used to analyze these dissipation mechanisms in prototypical surface dynamical processes such as gas-phase scattering and adsorption, diffusion, vibration, and surface reactions. In this topical review we provide an overview of modeling approaches to incorporate dissipation into corresponding dynamical simulations starting from coarse-grained effective theories to increasingly sophisticated methods. We illustrate these at the level of individual elementary processes through applications found in the literature, while specifically highlighting the persisting difficulty of gauging their performance based on experimentally accessible observables.

Great success has been achieved in the modeling of gas-surface elementary processes by the use of the Born-Oppenheimer approximation. However, in metal surfaces low energy electronic excitations are generated even by thermal and hyperthermal molecules due to the absence of band gaps in the electronic structure. This shows the importance of performing dynamical simulations that incorporate non-adiabatic effects to analyze in which way they affect most common gas-surface reactions. Here we review recent theoretical developments in this problem and their application to the study of the effect of electronic excitations in the adsorption and relaxation of atoms and molecules in metal surfaces, in scattering processes, and also in recombinative processes between impinging atoms and adsorbates at the surface. All these studies serve us to establish what properties of the gas-surface interaction favor the excitation of low-energy electron-hole pairs. A general observation is that the nature of these excitations usually requires long lasting interactions at the surface in order to observe deviations from the adiabatic behaviour. We also provide the basis of the local density friction approximation (LDFA) that have been used in all these studies, and show how it has been employed to perform ab initio molecular dynamics with electronic friction (AIMDEF). As a final remark, we will shortly review on recent applications of the LDFA to successfully simulate desorption processes induced by intense femtosecond laser pulses. [ABSTRACT FROM AUTHOR]

Elementary processes involving atomic and molecular species at surfaces are reviewed. The emphasis is on simple classical and quantum models that help to single out unifying dynamical themes and to identify the basic physical mechanisms that underlie the rich variety of phenomena of surface chemistry. Starting from an elementary description of the energy transfer between a gas-phase species and a surface-for both classical and quantum lattices-the key processes establishing the formation of an adsorbed phase (sticking, diffusion and vibrational relaxation) are discussed. This is instrumental for introducing the simplest chemical transformations involving adsorbed species and/or scattering of gas-phase molecules: Langmuir-Hinshelwood, Hot-Atom, and Eley-Rideal reactions forming complex molecules from elementary constituents, and dissociative chemisorption of molecules into smaller fragments. Applications are also provided illustrating the ideas developed along the way at work in real-world gas-surface problems. [ABSTRACT FROM AUTHOR]

Former calculations showed that atomic N incident at energies of a few eV on N-covered Ag(1 1 1) forms N 2 molecules by the Eley–Rideal (ER) mechanism, i.e. by direct pick-up of adsorbates. Here, we calculate the azimuthal angle distributions and the rovibrational energies of those ER products. We observe a non-trivial angle dependence that may result in very low in-plane ER yield for some given incident azimuthal angles. We find that most of the energy released upon N N bond formation, about 7 eV, is stored in the rovibrational degrees of freedom independently of the incidence energy considered. [ABSTRACT FROM AUTHOR]

We analyzed the dynamics of N atom scattering from N -covered Ag(1 1 1), using the generalized Langevin oscillator (GLO) method and a three-dimensional neural network potential energy surface. Two values for the mass of the surface oscillator were considered in the GLO model to account for the energy exchange with the surface, i.e., that of Ag and that of N. For these mass values different trends were found for the dependence of the ratio of the average final divided by the average initial translational energy on the scattering angle. Using the nitrogen mass gives a trend closer to the experimental results for the dependence of the energy of the in-plane scattered atoms on the scattering angle, but worse agreement with experiment for the angular distribution of the in-plane scattered atoms. Two different algorithms are applied to integrate the stochastic equations of motion in the presence of energy dissipation. Our calculations show that a trivially extended Bulirsch-Stoer algorithm is more efficient than an algorithm based on a Langevin Liouville operator splitting technique, in that it yields the same results with a much larger time step. [ABSTRACT FROM AUTHOR]

The interaction of water and surfaces, at molecular level, is of critical importance for understanding processes such as corrosion, friction, catalysis and mass transport. The significant literature on interactions with single crystal metal surfaces should not obscure unknowns in the unique behaviour of ice and the complex relationships between adsorption, diffusion and long-range inter-molecular interactions. Even less is known about the atomic-scale behaviour of water on novel, non-metallic interfaces, in particular on graphene and other 2D materials. In this manuscript, we review recent progress in the characterisation of water adsorption on 2D materials, with a focus on the nano-material graphene and graphitic nanostructures; materials which are of paramount importance for separation technologies, electrochemistry and catalysis, to name a few. The adsorption of water on graphene has also become one of the benchmark systems for modern computational methods, in particular dispersion-corrected density functional theory (DFT). We then review recent experimental and theoretical advances in studying the single-molecular motion of water at surfaces, with a special emphasis on scattering approaches as they allow an unparalleled window of observation to water surface motion, including diffusion, vibration and self-assembly., Competing Interests: Disclosure statement No potential conflict of interest was reported by the authors.

The creation of electronic excitations during the reaction of atomic hydrogen on and with coinage and noble metals has been studied using metal-insulator-metal heterostructures. A characteristic current trace is observed when the outer metal surface of the structure is exposed to a 20 s pulse of H atoms. Comparison to the chemical kinetics allows to disentangle the contributions from the different chemical processes to this current. In the case of the coinage metals studied the observation is interpreted to suggest that predominantly electrons excited in connection with the hydrogen recombination reaction are the source of the current. For Pt such phenomenon is not observed. This difference allows insights into the role of the transition state for the non-adiabaticity in this simple chemical reaction. [ABSTRACT FROM AUTHOR]

In honoring the seminal contribution of Henry Eyring and Michael Polanyi who first introduced the concept of potential energy surfaces (PESs) to describe chemical reactions in gas-phase [Z. Phys. Chem. 12, 279-311, (1931)], this work comes to review and assess state-of-the-art approaches towards first-principle based modeling in the field of gas-surface dynamics. Within the Born-Oppenheimer and frozen surface approximations, the O2-Ag(100) interaction energetics are used as a showcase system to accentuate the complex landscape exhibited by the PESs employed to describe the impingement of diatomics on metal substrates and draw attention to the far-from-trivial task of continuously representing them within all six molecular degrees of freedom. To this end, the same set of ab initio reference data obtained within Density Functional Theory (DFT) are continuously represented by two different state-of-the-art high-dimensional approaches, namely the Corrugation-Reducing Procedure and Neural Networks. Exploiting the numerically undemanding nature of the resulting representations, a detailed static evaluation is performed on both PESs based on an extensive global minima search. The latter proved particularly illuminating in revealing representation deficiencies which affect the dynamical picture yet go otherwise unnoticed within the so-called 'divide-and-conquer' approach. [ABSTRACT FROM AUTHOR]

Abstract: The dissociative chemisorption of hydrogen at metal surfaces is the first step in the surface chemistry of heterogeneous catalysis. Up to now, most of our understanding of this process has been obtained from sticking probability measurements. Recent experiments have shown that more detailed information on the potential energy surface (PES) governing the dissociative chemisorption of hydrogen can be obtained by employing a different technique, namely diffraction of monochromatic beams of molecular hydrogen and deuterium. In this paper, we review recent progress made by using this technique to characterize the corresponding PES for hydrogen dissociative chemisorption at metal surfaces. Elastic and rotationally inelastic diffraction (RID) peaks were observed in experiments performed on different single-crystal metal surfaces, ranging from non-reactive to very reactive ones, at incident energies between 20 and 200meV. Extrapolation of data points by using the Debye–Waller attenuation model makes comparison with theory possible. It is shown that an analysis of both H2 diffraction and RID intensities as a function of incident energy provides a very sensitive way to test the quality of ab initio determined six-dimensional PESs. This review provides an overview of the experimental procedures as well as on the theoretical tools presently being used. A comparison between theory and experiment is discussed for several illustrative examples. Perspectives for future experiments are discussed. [Copyright &y& Elsevier]

Abstract: A new generation of experimental techniques quantifies the gas–surface reactivity of polyatomic reactants prepared in a single quantum state. These experiments eliminate internal state averaging and permit reactivity measurements on molecules with well-defined internal and translational energy. Varying the identity of the selected vibrational and rotational state and the molecule’s translational energy reveals how energy in specific energetic coordinates promotes reaction. When applied to methane’s dissociative chemisorption, which is rate-limiting in the industrial steam reforming reaction, these experiments reveal the molecular basis for activation, and they provide detailed insight into energy flow dynamics prior to reaction. This review will focus on experiments that quantify the reactivity of methane prepared in select rovibrational quantum states via optical excitation in a supersonic molecular beam. An overview will provide context, and a survey of experimental methods will emphasize features unique to these experiments. A presentation and discussion of state-resolved beam-surface scattering studies of methane activation on Ni(111), Ni(100), and Pt(111) will highlight the mechanistic and dynamical insights that such studies can provide. For example, while C–H stretching excitation best promotes transition state access on Ni(111) and Ni(100), bending excitation also activates dissociation, suggesting that many different energetic coordinates contribute to reactivity. Among those states studied, non-statistical behavior, including vibrational mode-specific and even bond-selective chemistry, is widespread, which indicates that the assumptions underlying statistical rate theories do not apply to this reaction. We examine the relevant timescales for energy exchange and reaction to provide a plausible explanation for the observation of non-statistical behavior. Finally, we suggest how these methods, and the results they have produced, might guide future work in the field. [Copyright &y& Elsevier]

Abstract: Surface chemistry experiments can now quantify the reactivity of polyatomic reagents prepared in select vibrational states. These studies of vibrationally mediated chemistry are showing that the nature of the vibrational excitation, and not just its total energy, can play an important role in determining the rates and pathways of surface reactions. Such vibrational mode selective behavior results when the timescale for statistical redistribution of vibrational energy within the reaction complex is slower than reaction. This review surveys prior examples of mode selective reactivity on surfaces, and it emphasizes four aspects of experimental work published within the past year: the extension of earlier methane/nickel studies to another metal, the observation of vibrational mode selectivity in a precursor-mediated reaction, the demonstration of bond-selective control over a gas–surface reaction, and the outline of an emerging framework for understanding the origin of these non-statistical reaction patterns in surface chemistry. These studies impact our fundamental understanding of surface chemistry, and they point toward new strategies for controlling and manipulating reactivity in vapor deposition processes. [Copyright &y& Elsevier]

The collision of energetic gas phase particles with adsorbed species can induce a variety of processes. Events of this kind can play an important role in the mechanisms governing heterogeneous catalysis at high pressures and elevated temperatures. Two collision induced processes (CIP) are described in this article. The first process discussed is collision induced desorption (CID). The CID of N2 from Ru(001) is considered at both low and high coverage ranges. The interpretation of the experimental data using molecular dynamics (MD) simulations leads to the introduction of a new desorption mechanism involving surface corrugation and adsorbate frustrated rotational motion. The second process is collision induced migration (CIM), an event that has never been considered before neither experimentally nor theoretically. It is demonstrated, using MD simulations, that following energetic CIM, very long distances of more than 100A˚ can be covered by the adsorbates at low coverages. At high coverages, on the otherhand, these displacements become considerably shorter due to surface collisions with neighbors. [Copyright &y& Elsevier]