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The Ni_n (n =19, 20) +D₂ (v, j) collision systems have been studied to investigate the dependence of cluster reactivity on the cluster temperature and the initial rovibrational states of the molecule using quasiclassical molecular dynamics simulations. The clusters are described by an embedded atom potential, whereas the interaction between the molecule and the cluster is modeled by a LEPS (London–Eyring–Polani–Sato) potential energy function. Reaction (dissociative adsorption) cross-sections are computed as functions of the collision energy for different initial rovibrational states of the molecule and for different temperatures of the clusters. Rovibrational, temperature and size-dependent rate constants are also presented, and the results are compared with earlier studies. Initial vibrational excitation of the molecule increases the reaction cross-section more efficiently than the initial rotational excitation. The reaction cross-sections strongly depend on the collision energies below 0.1 eV.

In the present paper we review our findings on ethylene adsorption on clean and oxygen covered Ag(001) surfaces investigated by dosing the gas with a Supersonic Molecular Beam and analysing the adsorption state either by High Resolution Electron Energy Loss Spectroscopy or by High Resolution X Rays Photoemission Spectroscopy. The final adsorption state depends on the translational and on the internal energy of the gas-phase molecules and on the presence of defects. At low translational energy ethylene either physisorbs or very weakly chemisorbs at flat terrace sites. The physisorption probability is thereby hindered by rotational excitation. A more strongly bound, π bonded, state forms at higher translational energy, the activation barrier being related to the energy needed to form the relevant defect at which chemisorption takes place. A further even more strongly bound state forms only when dosing vibrationally excited molecules from the gas phase.

The chemisorption of one monolayer H atoms on Si(111) surface is studied by using the self-consistent, tight-binding, linear muffin-tin orbital method. Energies of adsorption systems, the layer projected density of states (LPDOS) and charge distributions are calculated. It is found that the adsorbed H atoms are more favorable on the top site with a distance of 0.185 nm above the Si surface. The LPDOS in the clean surface decreases significantly after H adsorption, since the dangling bonds of the surface atoms are partially saturated by the adsorbed H atoms.

Using the self-consistent tight-binding linear muffin-tin orbital method, we have investigated the electronic structure and adsorption properties of one monolayer Au atoms on a Si(111) surface. The total energies, the layer projected density of states and the charge distributions are calculated in detail. Our calculations show that the most stable position is on the interstitial center site above the Si(111) surface for the adsorbed Au atoms. It is possible for the Au atoms to sit below the Si surface, resulting in a Au–Si mixed layer at the Au/Si interface, which is in good agreement with the experimental results.

Recently [M. Kunat et al., Surf. Sci.474, 114 (2001)] a quenching of adsorbate-assisted adsorption ("autocatalytic adsorption") by defects has been observed for the system CO/Cu(110). A conceptually similar effect for CO adsorption on O–Ir(110) had additionally been reported before [U. Burghaus et al., Surf. Sci.384, L869 (1997)]. Presented is a simple Monte Carlo simulation (MCS) scheme which includes basically one free fit parameter and can reproduce both effects consistently.

Recent progress in the study of motions and reactions of single adsorbed molecules on metal surfaces induced by inelastic tunneling electrons with a scanning tunneling microscope (STM) is given an overview, with the focus on our current theoretical understanding of the elementary processes behind these phenomena. The selected topics include rotation and dissociation of O₂ on Pt(111), rotation of a C₂H(D)₂ on Cu(100), lateral hopping of CO on Pd(110), lateral translation and desorption of NH₃ on Cu(100), and controlled manipulation of chemical transformation as well as bimolecular reaction of coadsorbed species on metal surfaces. Brief descriptions are presented of how an adsorbate to overcome the potential barrier for motion and reaction by incoherent stepwise and coherent single multistep climbing of the vibrational ladders in the potential well along the reaction coordinate, and indirect excitation of the reaction coordinate mode via anharmonic coupling to the vibrational mode excited by tunneling current. Elementary processes of the mode-selective control of different motions are also discussed in conjunction with a recent experimental result of lateral hopping and desorption of a single NH₃ molecule on Cu(100). Although still at a premature stage, these novel phenomena open a new world of "nano-surface-science," in which the manipulation and reaction of single adsorbates, and synthesis of a new molecular system are realized by a selective excitation of the relevant vibrational mode by tunneling electrons with an STM.

Several molecular adsorption states are identified following ethylene adsorption on clean and hydrogen-covered Pd(111) using temperature-programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS). Di-σ-bonded ethylene forms on clean Pd(111) desorbing with an activation energy of 80 kJ/mol at low coverages. The strong intermolecular lateral interactions considerably reduce the desorption temperature at higher coverages. Π-bonded ethylene is formed on hydrogen-covered Pd(111), where the proportion of π-bonded species increases with hydrogen coverage. This species converts to the more stable di-σ-bonded species on heating. Ethane formation is detected in TPD from hydrogen-precovered Pd(111), which is predominantly formed by reaction with π-bonded ethylene.

We have modeled the dissociative chemisorption of water on the Si(100)-(2×1) surface using a generalized gradient approximation of density functional theory and a periodic slab model of the surface. For the energetically favorable structures, scanning tunneling microscope topographs of the filled states are simulated. These exhibit distinctively dark characteristics where water "islands" are formed, in agreement with experimental findings. In addition, they indicate that the hydrogen-atom and hydroxyl-radical adducts display somewhat different contrasts. Furthermore, in the case of a partial saturation of a Si dimer a prominent brightness is predicted for the unsaturated Si atoms if their dimer-forming counterparts are saturated by hydroxyl species, while in the case of hydrogen saturation the contrast is rather dim.

The adsorption of hydrogen atoms on the Ta(001)(1 × 1) surface is studied by first-principles density functional calculations within the generalized gradient approximation. It turns out that at 1 ML, coverage bridge site is energetically preferred over three-fold hollow site. This result does not support a recent LEED and HREELS observation that three-fold hollow site was preferred. The layer separation between the H atom and the topmost Ta atom is 1.12 Å and 0.55 Å for bridge and three-fold hollow site, respectively. Atomic distance between the H atom and the first layer Ta atom is 1.998 Å for bridge and 2.06 Å for three-fold site. The structural and energetic properties of H/W(100)(1 × 1) have been calculated. The results are shown to be in excellent agreement with available experimental and theoretical analysis. We find that the adsorption behavior of hydrogen on Ta(001)(1 × 1) surface is very similar to that of H/W(100) system.

The extract of Datura stramonium has been studied as a possible source of green inhibitor for corrosion of mild steel (MS) in HCl and H₂SO₄ media at different temperatures. The anticorrosion effect was evaluated by conventional weight loss studies, electrochemical studies viz., Tafel polarization, ac impedance, and SEM studies. The studies reveal that the plant extract acts as a good inhibitor in both the acid media and better in H₂SO₄ medium. Tafel polarization method indicate that the plant extract behaves as a mixed mode inhibitor. Double layer capacitance and charge transfer resistance values derived from Nyquist plots obtained from ac impedance studies give supporting evidence for the anticorrosive effect. The inhibitive effect may be attributed to the adsorption of the inhibitor on the surface of MS, following Temkin adsorption isotherm. Increase of inhibition efficiency with increase of temperature along with Ea values serve as a proof for chemisorption. SEM studies provide the confirmatory evidence for the protection of MS by the green inhibitor. The study reveals the potential of D. stramonium for combating corrosion which may be due to the adsorption of alkaloids and other phytoconstituents.

This paper describes the oxygen adsorption properties on magnesium oxide surface. The results are compared with theoretical adsorption kinetics. Temperature and time dependences of adsorption mechanisms and chemiluminescence are discussed.

In this paper, large-area chiral supramolecular self-assembly of 2,2’:6’,2”-terpyridine-4’-carboxylic acid (C${}_{16}$H${}_{11}$N₃O₂; Y) molecules on Cu(111) is studied using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The basic building blocks of such a self-assembled monolayer are triangular vortex-shaped supramolecular structures containing three twisted Y molecules. Chirality is maintained and transferred from one vortex to the adjacent vortex in successive molecular domains within the same atomic terrace. The twisted Y molecule, bridging two nearest-neighbor Cu atoms, is stabilized by symmetric Cu–O bonds on the surface. The near perpendicularity of these bonds to the surface is the main reason for the formation of “standing-up” Y molecules.

The adsorptions of sulfur atom on the Ir(100) surface at p(2 × 2) and c(2 × 2) phases were investigated by the density functional calculations within the generalized gradient approximation. The adsorption energy, adsorption geometry, work function change, and charge density distribution were analyzed. The hollow site was found to be the most stable, followed by the bridge and the top sites. The calculated adsorption geometries were in good agreement with the observed results. Particularly, it was found that the adsorption of S on Ir(100) caused a work function decrease. A charge accumulation at the interface between the S layer and the Ir substrate, which centered closer to the S atom, suggests a polar covalent bonding. Density of states (DOS) analysis showed that the adsorption of S induces a reduction of the surface Ir d-orbital DOS around the Fermi level.

Multistep dissociative chemisorption reactions of water with Pd₄ and Pd₇ clusters were studied using density functional theory. The adsorption energies and referred adsorption sites from water molecule (H₂O) to partially dissociative (H₂+O and OH+H), then to fully dissociative (O+H+H) configurations are carefully determined. It is found that the adsorption energies of three dissociative reactions are 5–6 times larger than that of water molecule. Atop sites of Pd₄ and Pd₇ clusters are found to be the most stable sites for the adsorbed H₂O molecule. For the coadsorption cases of partially and fully dissociated products, H₂ and OH molecules preferably tend to bind at the low coordination (atop or bridge) sites, and O and H atoms prefer to adsorb on the high coordination (hollow) sites. It is also found that the most favorable adsorption sites for the molecular adsorbates (H₂O, H₂ and OH) are adjacent to the Pd atoms with the largest site-specific polarizabilities. Therefore, site-specific polarizability is a good predictor of the favorable adsorption sites for the weakly bound molecules. The different directions of charge transfer between the Pd clusters and the adsorbate(s) is observed. Furthermore, the processes of the adsorption, dissociation, and the dissociative products diffusion of H₂O are analyzed.

New polymeric adsorbents (ZH-02, ZH-03) containing benzoyl group for adsorbing and removing 4-methylaniline from its aqueous solutions were prepared. Studies on the isotherms and the comparison of desorption conditions evidenced through the adsorption of 4-methylaniline in water onto ZH-02 and ZH-03, namely that there are chemisorption's transitions at a proper higher temperature. Mini-column adsorption studies of 4-methylaniline on XAD-4, ZH-02 and ZH-03 at 288 K show that the breakthrough capacities are 2.39, 2.99 and 3.19 mmol/g and the total capacities are 3.45, 3.92 and 4.35 mmol/g, respectively.

A hypercrosslinked adsorption resin (ZH-05) modified by N-acetylaniline in the post crosslinking process was prepared. The adsorption properties of ZH-05 toward 2,4-dichlorophenol in comparison with granular activated carbon (GAC) and Amberlite XAD-4 were observed. The present study mainly focuses on the static equilibrium adsorption behaviors, desorption profiles and the proof of chemisorption. The results show that the Langmuir equation can give a perfect fitting to experimental data, and high temperature was favorable for adsorption of 2,4-dichlorophenol on ZH-05. A related equation was used to correlate the amount of chemisorption and the suppositional chemisorption equilibrium concentration of adsorbate in aqueous solution. The adsorption capacities from different ranges of temperature and the static desorption experiment both reveal the same conclusion, i.e., the adsorption of 2,4-dichlorophenol from water on ZH-05 is a coexistent process of physical adsorption and chemical transition as on GAC.

Magnetic molecules are auspicious candidates to act as functional units in molecular spintronics. Integrating molecules into a device environment providing mechanical support and electrical contacts requires their deposition as intact entities onto substrates. Thermal sublimation is a very clean deposition process that, however, thermally decomposes molecules of insufficient stability leading to the deposition of molecular fragments. Here, we show that the molecule-surface interaction of chemisorbed molecules affects the intramolecular bonding and can lead depending on the surface reactivity to either molecular decomposition or enhanced stability. We study the integrity of single bis(phthalocyaninato)-neodymium(III) molecules (NdPc₂) deposited by sublimation on differently reactive surfaces, namely Au(111), Cu(100), and two atomic layers of Fe on W(110), on the single molecular level by scanning tunneling microscopy (STM) and spectroscopy. We find a strongly substrate-dependent tendency of the NdPc₂ molecules to decompose into two Pc molecules. Surprisingly, the most reactive Fe/W(110) surface shows the lowest molecular decomposition probability, whereas there are no intact NdPc₂ molecules at all on the least reactive Au(111) surface. We attribute these findings to substrate-dependent partial charge transfer from the substrate to the Pc ligands of the molecule, which strengthens the intramolecular bonding mediated predominantly by electrostatic interaction.

A series of quartz surfaces were modified with a series of crosslinkers and functional groups in order to obtain an azide-terminated monolayer, which was then used to immobilize pyrene onto the surface via alkyne-azide "click" chemistry. During the course of the immobilization, different ratios of tert-butyl diphenyl chlorosilane were used to control the distribution and hence the photophysical properties of the pyrene on the surface. The preparative surface reactions and photophysical properties were investigated with contact angle, X-ray photoelectron spectroscopy, UV-visible absorption and emission spectroscopy. High surface coverage was achieved of just under 1molecule per nm². At this coverage all emission from the pyrene was in the form of excimer emission. Excimer emission dominated at all surface coverages greater than 0.45 molecules per nm². Below this coverage the monomer emission could also be observed. The conclusions that can be drawn are important for understanding the interactions of neighboring molecules in molecular monolayers. Our results suggest that at high surface coverage a substantial number of the pyrene molecules are already close enough to their neighbors that pairs of them can be directly excited to form excimer with no requirement for diffusion. This can be stated because the long wavelength end of the pyrene absorption and excitation spectra show a broad tail that is assigned to a charge transfer band resulting from an electron being directly transferred from a ground state pyrene to a neighboring pyrene molecule. Furthermore, absorption spectra shifts also indicate that the pyrene molecules undergo some interactions on the surface when they are closely packed.

In the age when the miniaturization trend that has driven the semiconductor industry is reaching its limits, organic modification of semiconductors is emerging as a field that could give much-needed impetus. We review the current state of understanding of the functionalization of C(100), Si(100), and Ge(100) surfaces through chemisorption of alkenes and alkynes, focusing on adsorbate structural control. While reactions on C(100) show most of the properties expected for concerted cycloaddition reactions such as [2+2] and [4+2] (Diels–Alder) processes, reactions on Si(100) present a wide range of variant behavior, including in some cases the prominence of non-cycloaddition products. More general stepwise free-radical addition processes are seen to provide a better description of reactions on Si(100), their prominence being attributed to either the non-existence or ineffectiveness of π bonding within surface silicon dimers. The investigations of these systems provide not only insight into driving mechanisms for chemisorption but also motivation for the development of new techniques of organic functionalization on semiconductors.