2017 |
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Morisset, S., Rougeau, N., & Teillet-Billy, D. (2017). Influence of a graphene surface on the first steps of the hydrogenation of a coronene molecule. Chemical Physics Letters, 679, 225–232.
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Wakelam, V., Bron, E., Cazaux, S., Dulieu, F., Gry, C., Guillard, P., Habart, E., Hornekær, L., Morisset, S., Nyman, G., Pirronello, V., Price, S. D., Valdivia, V., Vidali, G., & Watanabe, N. (2017). H 2 formation on interstellar dust grains: The viewpoints of theory, experiments, models and observations. Molecular Astrophysics, 9, 1–36.
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2016 |
Cazaux, S., Boschman, L., Rougeau, N., Reitsma, G., Hoekstra, R., Teillet-Billy, D., Morisset, S., Spaans, M., & Schlatholter, T. (2016). The sequence to hydrogenate coronene cations: A journey guided by magic numbers. Sci Rep, 6, 19835.
Résumé: The understanding of hydrogen attachment to carbonaceous surfaces is essential to a wide variety of research fields and technologies such as hydrogen storage for transportation, precise localization of hydrogen in electronic devices and the formation of cosmic H2. For coronene cations as prototypical Polycyclic Aromatic Hydrocarbon (PAH) molecules, the existence of magic numbers upon hydrogenation was uncovered experimentally. Quantum chemistry calculations show that hydrogenation follows a site-specific sequence leading to the appearance of cations having 5, 11, or 17 hydrogen atoms attached, exactly the magic numbers found in the experiments. For these closed-shell cations, further hydrogenation requires appreciable structural changes associated with a high transition barrier. Controlling specific hydrogenation pathways would provide the possibility to tune the location of hydrogen attachment and the stability of the system. The sequence to hydrogenate PAHs, leading to PAHs with magic numbers of H atoms attached, provides clues to understand that carbon in space is mostly aromatic and partially aliphatic in PAHs. PAH hydrogenation is fundamental to assess the contribution of PAHs to the formation of cosmic H2.
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2015 |
Houplin, J., Amiaud, L., Sedzik, T., Dablemont, C., Teillet-Billy, D., Rougeau, N., & Lafosse, A. (2015). A combined DFT/HREELS study of the vibrational modes of terphenylthiol SAMs. Eur. Phys. J. D, 69(9), 9 pp.
Résumé: Self-assembled monolayers of p-terphenylthiol (TPT, HS-(C6H4)(2)-C6H5) deposited onto gold can serve as model systems for aromatic lithography resists. Such thin molecular films are suitably probed using high resolution electron energy loss spectroscopy, due to its high surface sensitivity. Extended energy loss spectra were measured at different probing energies. The TPT monolayer overlapping.(CH) stretching modes could be modelled by a single effective anharmonic oscillator sustained by a Morse potential energy curve, thanks to the resonant excitation of the associated overtone series at 6 eV. A remarkably good agreement was obtained between the TPT monolayer energy loss spectrum and the computer-simulated infrared vibrational spectrum of the isolated TPT molecule. Density Functional Theory calculations for TPT, fully deuterated TPT and benzenethiol isolated molecules were performed with the exchange correlation functional B3LYP and a dispersion correction, using a triple zeta+ polarisation basis set. By comparing the vibrational patterns obtained for these parent systems, (re-) assignments of all the features observed in the TPT self-assembled monolayer energy loss spectrum are discussed. The obtained vibrational assignments can be confidently transposed to other related systems, such as benzenethiol and biphenyl self-assembled monolayers.
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2014 |
Nave, S., Tiwari, A. K., & Jackson, B. (2014). Dissociative chemisorption of methane on Ni and Pt surfaces: mode-specific chemistry and the effects of lattice motion. J Phys Chem A, 118(41), 9615–9631.
Résumé: The dissociative chemisorption of methane on metal surfaces is of great practical and fundamental interest. Not only is it the rate-limiting step in the steam re-forming of natural gas, but also the reaction exhibits interesting mode-specific behavior and a strong dependence on the temperature of the metal. Electronic structure methods are used to explore this reaction on various Ni and Pt surfaces, with a focus on how the transition state is modified by motion of the metal lattice atoms. These results are used to construct models that explain the strong variation in reactivity with substrate temperature, shown to result primarily from changes in the dissociation barrier height with lattice motion. The dynamics of the dissociative chemisorption of CH4 on Ni and Pt is explored, using a fully quantum approach based on the reaction path Hamiltonian that includes all 15 molecular degrees of freedom and the effects of lattice motion. Agreement with experiment is good, and vibrational excitation of the molecule is shown to significantly enhance reactivity. The efficacy for this is examined in terms of the vibrationally nonadiabatic couplings, mode softening, mode symmetry, and energy localization in the reactive bond.
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Ouvrard, A., Wang, J., Ghalgaoui, A., Nave, S., Carrez, S., Zheng, W., Dubost, H., & Bourguignon, B. (2014). CO Adsorption on Pd(100) Revisited by Sum Frequency Generation: Evidence for Two Adsorption Sites in the Compression Stage. J. Phys. Chem. C, 118(34), 19688–19700.
Résumé: Sum frequency generation (SFG) and low-energy electron diffraction (LEED) have been used to revisit CO adsorption on Pd(100) from very low coverages up to saturation at 300 K Below 0.5 ML, variations of SFG frequency and intensity with coverage are consistent with IRAS results from the literature. Novel observations are done above 0.5 ML, where the CO adlayer compression takes place. The existing compression model postulates the coexistence of compressed and uncompressed CO. We observe two bands in the spectral region of bridge sites and assign them to compressed and uncompressed CO. Both types of CO behave very differently: the molecular hyperpolarizability at compressed sites is smaller by a factor of 2 than at uncompressed sites. The frequency of uncompressed CO red-shifts during compression as the partial coverage decreases, while that of compressed CO continues to blue-shift as coverage increases. In the time domain, the coexistence of compressed and uncompressed sites results in oscillations in the decay of SFG intensity. A strong decrease from 690 to 222 fs of the phase relaxation time of uncompressed CO is observed during compression, indicating a stronger coupling to the substrate. These results are complemented by calculations of dipole-dipole interactions and DFT VASP calculations. While continuing blue-shift of compressed sites reflects a combination of increasing dipolar coupling and chemisorption change with coverage like below 0.5 ML, the very large red-shift amplitude of uncompressed CO indicates a large chemical contribution opposite to compressed CO. DFT VASP calculations allow us to follow the surface structure evolution from 0.5 to 0.67 ML and CO frequency changes with coverage. Pd atoms below compressed CO rows are pushed up, and compressed CO is tilted by 8-90 with respect to the surface normal. A frequency split between compressed and uncompressed CO is found in agreement with experimental data. These results suggest that while compressed CO is less strongly bonded as compression proceeds the remaining uncompressed CO is more strongly bonded.
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2013 |
Garcia-Gil, S., Teillet-Billy, D., Rougeau, N., & Sidis, V. (2013). H Atom Adsorption on a Silicate Surface: The (010) Surface of Forsterite. JOURNAL OF PHYSICAL CHEMISTRY C, 117(24), 12612–12621.
Résumé: We present a first-principles computational study of the interaction of an H
atom with the (010) surface of forsterite (Mg2SiO4). Periodic DFT-GGA calculations (PBE)are carried out using the SIESTA code with core pseudopotentials and TZP localized basis sets. Potential energy curves are determined for the approach of the H atom toward different sites of the surface: atop, near, or in between the O, Mg, and Si atoms. An outer adsorption well is found for all investigated sites; it is deepest (162 meV) at a so-called “displaced Mg−O bridge” position. The binding at this well is of the “weak chemisorption”/“strongphysisorption” type. An inner stronger chemisorption well (670 meV deep) exists exclusivelynear an O site but not strictly atop. Depending on the path, we find activation barriers (25−170 meV high) against chemisorption, the lowest of these occurs for the top O site.General trends of the computed interaction energies qualitatively agree with the QM/MM results of Goumans et al. [Mon. Not. R. Astron. Soc. 2009, 393, 1403], but adsorption bindingenergies and barrier heights differ significantly.
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Han, D., Nave, S., & Jackson, B. (2013). Dissociative chemisorption of methane on Pt(110)-(1x2): effects of lattice motion on reactions at step edges. J Phys Chem A, 117(36), 8651–8659.
Résumé: The dissociative chemisorption of methane on Pt(110)-(1x2) is examined, with a focus on how the reaction dynamics are modified by the motion of the lattice atoms. The barriers to dissociation are found to be lowest at the step edges. The relaxation of the lattice in the presence of the dissociating molecule is found to be far more complicated than on the smooth surfaces of Pt and Ni. The dissociative sticking probabilities are computed using a full-dimensional treatment based on the reaction path Hamiltonian that includes all 15 molecular degrees of freedom and the effects of lattice motion. The potential energy surface and all parameters in our model are computed from first principles. The effects of lattice motion are strong, but not significantly larger than for dissociation on smoother surfaces. Vibrational excitation of the molecule can significantly enhance reactivity, though this effect varies from mode to mode. Agreement with recent experiments with regard to the variation of reactivity with translational energy and substrate temperature is good.
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Jackson, B., & Nave, S. (2013). The dissociative chemisorption of methane on Ni(111): The effects of molecular vibration and lattice motion. JOURNAL OF CHEMICAL PHYSICS, 138(17), 174705.
Résumé: We examine the dissociative chemisorption of methane on a Ni(111) surface, using a fully quantum approach based on the Reaction Path Hamiltonian that includes all 15 molecular degrees of freedom and the effects of lattice motion. The potential energy surface and all parameters in our model are computed from first principles. Vibrational excitation of the molecule is shown to significantly enhance the reaction probability, and the efficacy for this is explained in terms of the vibrationally non-adiabatic couplings, vibrational mode softening, and mode symmetry. Agreement with experimental data for molecules initially in the ground and 1nu3 state is good, and including lattice anharmonicity further improves our results. The variation of the dissociation probability with substrate temperature is well reproduced by the model, and is shown to result primarily from changes in the dissociation barrier height with lattice motion. The enhancement of dissociative sticking with substrate temperature is particularly strong for processes that would otherwise have insufficient energy to surmount the barrier. Our model suggests that vibrationally excited molecules are likely to dominate the “laser off” dissociative sticking at high nozzle temperatures.
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2012 |
Bergeron, H., Curado, E. M. F., Gazeau, J. P., & Rodrigues, L. M. C. S. (2012). Generating functions for generalized binomial distributions. JOURNAL OF MATHEMATICAL PHYSICS, 53(10), 103304.
Résumé: In a recent article generalization of the binomial distribution associated with a sequence of positive numbers was examined. The analysis of the nonnegativeness of the formal probability distributions was a key point to allow to give them a statistical interpretation in terms of probabilities. In this article we present an approach based on generating functions that solves the previous difficulties. Our main theorem makes explicit the conditions under which those formal probability distributions are always non-negative. Therefore, the constraints of non-negativeness are automatically fulfilled giving a complete characterization in terms of generating functions. A large number of analytical examples becomes available. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4757601]
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Bergeron, H., Siegl, P., & Youssef, A. (2012). New SUSYQM coherent states for Poschl-Teller potentials: a detailed mathematical analysis. JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL, 45(24).
Résumé: In a recent short note (Bergeron et al 2010 Europhys. Lett. 92 60003), we have presented the good properties of a new family of semi-classical states for Poschl-Teller potentials. These states are built from a supersymmetric quantum mechanics (SUSYQM) approach and the parameters of these 'coherent' states are points in the classical phase space. In this paper, we develop all the mathematical aspects that have been left out of the previous paper (proof of the resolution of unity, detailed calculations of the quantized version of classical observables and mathematical study of the resulting operators: problems of domains, self-adjointness or self-adjoint extensions). Some additional questions such as asymptotic behavior are also studied. Moreover, the framework is extended to a larger class of Poschl-Teller potentials. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to 'Coherent states: mathematical and physical aspects'.
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Chaabouni, H., Bergeron, H., Baouche, S., Dulieu, F., Matar, E., Congiu, E., Gavilan, L., & Lemaire, J. L. (2012). Sticking coefficient of hydrogen and deuterium on silicates under interstellar conditions. ASTRONOMY & ASTROPHYSICS, 538, A128.
Résumé: Context. Sticking of H and D atoms on interstellar dust grains is the first step in molecular hydrogen formation, which is a key reaction in the interstellar medium. Isotopic properties of the sticking can have an incidence on the observed HD molecule. Aims. After studying the sticking coefficients of H-2 and D-2 molecules on amorphous silicate surfaces experimentally and theoretically, we extrapolate the results to the sticking coefficient of atoms and propose a formulae that gives the sticking coefficients of H and D on both silicates and icy dust grains. Methods. In our experiments, we used the King and Wells method for measuring the sticking coefficients of H-2 and D-2 molecules on a silicate surface held at 10 K. It consists of measuring with a QMS (quadrupole mass spectrometer) the signals of H-2 and D-2 molecules reflected by the surface during the exposure of the sample to the molecular beam at a temperature ranging from 20 K to 340 K. We tested the efficiency of a physical model, developed previously for sticking on water-ice surfaces. We applied this model to our experimental results for the sticking coefficients of H-2 and D-2 molecules on a silicate surface and estimated the sticking coefficient of atoms by a single measurement of atomic recombination and propose an extrapolation. Results. Sticking of H, D, HD, H-2, and D-2 on silicates grains behaves the same as on icy dust grains. The sticking decreases with the gas temperature, and is dependent on the mass of the impactor. The sticking coefficient for both surfaces and impactors can be modeled by an analytical formulae S (T) = S-0(1 + beta T/ T-0)/(1 + T/T-0)(beta), which describes both the experiments and the thermal distribution expected in an astrophysical context. The parameters S-0 and T-0 are summarized in a table. Conclusions. Previous estimates for the sticking coefficient of H atoms are close to the new estimation; however, we find that, when isotopic effects are taken into account, the sticking coefficient variations can be as much as a factor of 2 at T = 100 K.
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Garcia-Gil, S., Garcia, A., & Ordejon, P. (2012). Calculation of core level shifts within DFT using pseudopotentials and localized basis sets. EUROPEAN PHYSICAL JOURNAL B, 85(7), 239.
Résumé: The calculation of core level shifts can be done in the context of density functional theory (DFT) using different approaches and physical approximations to the photoemission process. The initial state and the Delta SCF approximations are the most commonly used ones. Here, we describe the details of their implementation in the context of DFT using pseudopotentials and localized atomic orbitals as a basis set, and in particular as applied to the Siesta code. We give a full account of the technicalities involved in these calculations, including the details of the ionic pseudopotential generation, basis sets, charge states and reference potential. We test the method by computing the core level shifts of the Si 2p level for a series of molecules and the p(2x2) asymmetric- dimer reconstruction of the Si(001) surface.
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2011 |
Cazaux, S., Morisset, S., Spaans, M., & Allouche, A. (2011). When sticking influences H-2 formation. ASTRONOMY & ASTROPHYSICS, 535, A27.
Résumé: Aims. Because of their catalytic properties, interstellar dust grains are crucial to the formation of H-2, the most abundant molecule in the Universe. The formation of molecular hydrogen strongly depends on the ability of H atoms to stick on dust grains. In this study we determine the sticking coefficient of H atoms chemisorbed on graphitic surfaces, and estimate its impact on the formation of H-2. Methods. The sticking probability of H atoms chemisorbed onto graphitic surfaces is obtained using a mixed classical-quantum dynamics method. In this, the H atom is treated quantum-mechanically and the vibrational modes of the surface are treated classically. The implications of sticking for the formation of H-2 are addressed by using kinetic Monte Carlo simulations that follow how atoms stick, move and associate with each other on dust surfaces of different temperature. Results. In our model, molecular hydrogen forms very efficiently for dust temperatures lower than 15 K through the involvement of physisorbed H atoms. At dust temperatures higher than 15 K and gas temperatures lower than 2000 K, H-2 formation differs strongly if the H atoms coming from the gas phase have to cross a square barrier (usually considered in previous studies) or a barrier obtained by density functional theory (DFT) calculations to become chemisorbed. The product of the sticking times efficiency can be increased by many orders of magnitude when realistic barriers are considered. If graphite phonons are taken into account in the dynamics calculations, then H atoms stick better on the surface at high energies, but the overall H-2 formation efficiency is only slightly affected. Our results suggest that H-2 formation can proceed efficiently in photon-dominated regions, X-ray dominated regions, hot cores and in the early Universe when the first dust is available.
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Jackson, B., & Nave, S. (2011). The dissociative chemisorption of methane on Ni(100): Reaction path description of mode-selective chemistry. JOURNAL OF CHEMICAL PHYSICS, 135(11), 114701.
Résumé: We derive a model for the dissociative chemisorption of methane on a Ni(100) surface, based on the reaction path Hamiltonian, that includes all 15 molecular degrees of freedom within the harmonic approximation. The total wavefunction is expanded in the adiabatic vibrational states of the molecule, and close-coupled equations are derived for wave packets propagating on vibrationally adiabatic potential energy surfaces, with non-adiabatic couplings linking these states to each other. Vibrational excitation of an incident molecule is shown to significantly enhance the reactivity, if the molecule can undergo transitions to states of lower vibrational energy, with the excess energy converted into motion along the reaction path. Sudden models are used to average over surface impact site and lattice vibrations. Computed dissociative sticking probabilities are in good agreement with experiment, with respect to both magnitude and variation with energy. The v(1) vibration is shown to have the largest efficacy for promoting reaction, due to its strong non-adiabatic coupling to the ground state, and a significant softening of the vibration at the transition state. Most of the reactivity at 475 K is shown to result from thermally assisted over-the-barrier processes, and not tunneling. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3634073]
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Rougeau, N., Teillet-Billy, D., & Sidis, V. (2011). On the PES for the interaction of an H atom with an H chemisorbate on a graphenic platelet. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13(39), 17579–17587.
Résumé: Motivated by the problem of H(2) formation in diffuse clouds of the interstellar medium (ISM), we study the effect of including van der Waals-type corrections in DFT calculations on the entrance PES of the Eley-Rideal reaction H(b) + H(a)-GR -> H(b)-H(a) + GR for a graphenic surface GR. The present calculations make use of the PBE-D3 dispersion corrected functional of Grimme et al. (2010) and are carried out on cluster models of graphenic surfaces: C(24)H(12) and C(54)H(18). To assess the soundness of the chosen functional we start by revisiting the H-GR adsorption potential. We find a satisfactory on top physisorption well (43-48 meV) correctly located at an H-GR distance of 3 angstrom. We then revisit the H(b)-H(a)-GR system using both the PW91 and PBE functionals. Our calculations do not reproduce the tiny potential barrier reported earlier for large H(b) distances from the surface. The barrier in the calculations of Sidis et al. (2000) and Morisset et al. (2003, 2004) has been traced to their previous use of an LSDA + POSTSCF PW91 procedure rather than the genuine PW91 one. The new PBE-D3 PES for the H(b)-H(a)-GR system is reported as a function of the H(b) distance to the surface and its impact parameter relative to the H(a) chemisorbate for the so-called “fixed puckered” (“diabatic” or “sudden”) approach. The results are discussed in relation to recent experimental and theoretical work.
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2010 |
Bergeron, H., Gazeau, J. - P., Siegl, P., & Youssef, A. (2010). Semi-classical behavior of Poschl-Teller coherent states. EPL, 92(6), 60003.
Résumé: We present a construction of semi-classical states for Poschl-Teller potentials based on a supersymmetric quantum mechanics approach. The parameters of these “coherent” states are points in the classical phase space of these systems. They minimize a special uncertainty relation. Like standard coherent states they resolve the identity with a uniform measure. They permit to establish the correspondence (quantization) between classical and quantum quantities. Finally, their time evolution is localized on the classical phase space trajectory. Copyright (C) EPLA, 2010
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Ivanovskaya, V. V., Zobelli, A., Teillet-Billy, D., Rougeau, N., Sidis, V., & Briddon, P. R. (2010). Enhanced H-2 catalytic formation on specific topological defects in interstellar graphenic dust grain models. PHYSICAL REVIEW B, 82(24), 245407.
Résumé: First-principles models of the formation of H-2 on interstellar media carbonaceous grains are usually concerned with processes occurring on ideal graphenic surfaces. Until now these models are unable to explain the formation of molecular hydrogen due to the presence of absorption barriers that cannot be overcome at the low temperatures of the interstellar media. We propose an approach emphasizing the role of specific topological defects for molecular hydrogen catalysis at interstellar dust grain models. Using the nudged elastic band method combined with density-functional techniques, we obtain the full catalytic cycle for the formation of the H-2 molecule on complex carbon topologies involving the presence of pentagonal rings and C adatoms. Depending on structures, reaction paths can be barrierless or have adsorption barriers as low as 10(-3)-10(-2) eV, which might be easily overcome at the temperatures of the interstellar medium. Such low adsorption barriers indicate that specific carbon grains topological defects are preferential sites for the molecular hydrogen formation in the interstellar medium.
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Ivanovskaya, V. V., Zobelli, A., Teillet-Billy, D., Rougeau, N., Sidis, V., & Briddon, P. R. (2010). Hydrogen adsorption on graphene: a first principles study. EUROPEAN PHYSICAL JOURNAL B, 76(3), 481–486.
Résumé: We present a systematic ab initio study of atomic hydrogen adsorption on graphene. The characteristics of the adsorption process are discussed in relation with the hydrogenation coverage. For systems with high coverage, the resultant strain due to substrate relaxation strongly affects H atom chemisorption. This leads to local structural changes that have not been pointed out to date, namely localized surface curvature. We demonstrate that the hydrogen chemisorption energy barrier is independent of the optimization technique and system size, being associated with the relaxation and rehybridization of the sole adsorbent carbon atom. On the other hand, the H desorption barrier is very sensitive to a correct structural relaxation and is also dependent on the degree of system hydrogenation.
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Matar, E., Bergeron, H., Dulieu, F., Chaabouni, H., Accolla, M., & Lemaire, J. L. (2010). Gas temperature dependent sticking of hydrogen on cold amorphous water ice surfaces of interstellar interest. JOURNAL OF CHEMICAL PHYSICS, 133(10), 104507.
Résumé: Using the King and Wells method, we present experimental data on the dependence of the sticking of molecular hydrogen and deuterium on the beam temperature onto nonporous amorphous solid water ice surfaces of interstellar interest. A statistical model that explains the isotopic effect and the beam temperature behavior of our data is proposed. This model gives an understanding of the discrepancy between all known experimental results on the sticking of molecular hydrogen. Moreover, it is able to fit the theoretical results of Buch et al. [Astrophys. J. 379, 647 (1991)] on atomic hydrogen and deuterium. For astrophysical applications, an analytical formula for the sticking coefficients of H, D, H(2), D(2), and HD in the case of a gas phase at thermal equilibrium is also provided at the end of the article. (C) 2010 American Institute of Physics. [doi:10.1063/1.3484867]
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Morisset, S., Ferro, Y., & Allouche, A. (2010). Study of the sticking of a hydrogen atom on a graphite surface using a mixed classical-quantum dynamics method. JOURNAL OF CHEMICAL PHYSICS, 133(4), 044508.
Résumé: The sticking of one hydrogen atom chemisorbed on the (0001) graphite surface is investigated using a mixed classical-quantum method. The phonon modes of the system in the collinear scattering approach are included in the dynamics calculations. The vibrational degrees of freedom of the surface (phonons) are treated classically, while the H-surface motion is treated using a one-dimensional quantum wave packet propagation method. The sticking probabilities are calculated and the individual contributions of the phonon bands to the collision dynamics are analyzed for surface temperatures of 10, 150, and 300 K and hydrogen kinetic energies ranging from 0.13 to 1.08 eV. An analytical form of the sticking probability as a function of the surface temperature is also proposed. (C) 2010 American Institute of Physics. [doi:10.1063/1.3463001]
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Nave, S., & Jackson, B. (2010). Vibrational mode-selective chemistry: Methane dissociation on Ni(100). PHYSICAL REVIEW B, 81(23), 233408.
Résumé: A first-principles full-dimensional model for CH(4) dissociation on Ni(100) is derived using a reaction path formulation. Vibrational excitation of the methane is found to significantly enhance reactivity when the molecule undergoes transitions to the ground or lower-energy vibrational states with the excess energy converted into motion along the reaction path. The nu(1) vibration has the largest efficacy for promoting reaction, with the nu(3) efficacy smaller, but significant.
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Nave, S., Tiwari, A. K., & Jackson, B. (2010). Methane dissociation and adsorption on Ni(111), Pt(111), Ni(100), Pt(100), and Pt(110)-(1x2): Energetic study. JOURNAL OF CHEMICAL PHYSICS, 132(5).
Résumé: We use density functional theory to examine 24 transition states for methane dissociation on five different metal surfaces. In our calculations, the nonlocal exchange-correlation effects are treated within the generalized gradient approximation using the Perdew-Burke-Ernzerhof functional. In all cases, the minimum energy path for dissociation is over a top site. The barriers are large, 0.66-1.12 eV, and relatively insensitive to the rotational orientation of the (nonreacting) methyl group and the azimuthal orientation of the reactive C-H bond. There is a strong preference on the Pt surfaces for the methyl fragment to bond on the top site, while on the Ni surfaces there is a preference for the hollow or bridge sites. Thus, during the dissociation on Pt, only the low mass H atom needs to significantly move or tunnel, while on Ni, both the dissociating H and the methyl fragment move away from the top site. For all 24 configurations there is a strong force at the transition state to pucker the metal atom over which the reaction occurs. The resulting magnitude of the variation in the barrier height with the motion of this atom varies a bit from surface-to-surface, but is of the order of 1 eV/angstrom. We derive a model for the effective reaction barrier height that includes the effects of lattice motion and substrate temperature and compare with recent experiments and other theoretical studies. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3297885]
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Sizun, M., Bachellerie, D., Aguillon, F., & Sidis, V. (2010). Investigation of ZPE and temperature effects on the Eley-Rideal recombination of hydrogen atoms on graphene using a multidimensional graphene-H-H potential. Chem. Phys. Lett., 498(1-3), 32–37.
Résumé: We study the Eley-Rideal recombination of H atoms on graphene under the physical conditions of the interstellar medium. Effects of the ZPE motions of the chemisorbed H atom and of the graphene thermal motions are investigated. Classical molecular dynamics calculations undertaken with the multidimensional potential of Bachellerie et al. [Phys. Chem. Chem. Phys. 11 (2009) 2715] are reported. The ZPE effects are the strongest. The closer the collision energy is to the classical reaction threshold the more sizeable the effects. The quantum reaction cross section is also estimated below and above the classical threshold using a capture model. (C) 2010 Elsevier B.V. All rights reserved.
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Teillet-Billy, D., Rougeau, N., Ivanovskaya, V. V., & Sidis, V. (2010). Interaction of Atoms with Graphenic-Type Surfaces for the Chemistry of the Interstellar Medium: New Properties of H Dimers on the Surface. INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 110(12), 2231–2236.
Résumé: Following the works of Rougeau et al. (Chem Phys Lett 2006, 431,135) and Ferro et al. (Phys Rev B 2008, 78, 085417) on the one-sided double chemisorption of H atoms on graphenic platelets, we investigate the two-sided double chemisorption using DFT-GGA PW91 calculations. Equilibrium characteristics and potential energy curves for chemisorption are reported for the ortho, meta, para, and bottom positions. Contrary to the one-sided case, the two-sided ortho chemisorption, as well as the bottom position, is barrier-less, whereas the two-sided para chemisorption exhibits an activation barrier. The highest occupied Kohn-Sham orbital (HOKSO) of the H-graphene radical is shown to signal the privileged barrier-less double chemisorption sites. (C) 2010 Wiley Periodicals, Inc. Int J Quantum Chem 110:2231-2236, 2010
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Tiwari, A. K., Nave, S., & Jackson, B. (2010). The temperature dependence of methane dissociation on Ni(111) and Pt(111): Mixed quantum-classical studies of the lattice response. JOURNAL OF CHEMICAL PHYSICS, 132(13), 134702.
Résumé: The barrier to the dissociative adsorption of methane on metal surfaces is generally large, and its height can vary with the motion of the lattice atoms. One fully quantum and three different mixed quantum-classical approaches are used to examine this reaction on Ni(111) and Pt(111) surfaces, using potential energy surfaces derived from density functional theory. The three approximate methods are benchmarked against the exact quantum studies, and two of them are shown to work reasonably well. The mixed models, which treat the lattice motion classically, are used to examine the lattice response during the reaction. It is found that the thermal motion of the lattice atoms strongly modifies the reactivity, but that their motion is not significantly perturbed. Based on these results, new models for methane reactions are proposed based on a sudden treatment of the lattice motion and shown to agree well with the exact results. In these new models, the reaction probability at different surface temperatures is computed from static surface reaction probabilities, allowing for a quantum calculation of the reaction probability without having to explicitly treat the motion of the heavy lattice atoms.
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2009 |
Bachellerie, D., Sizun, M., Aguillon, F., & Sidis, V. (2009). Effects of a Nonrigid Graphene Surface on the LH Associative Desorption of H Atoms and on the Deexcitation of Nascent H-2 Molecules Colliding with Model Walls of Carbonaceous Porous Material. J. Phys. Chem. A, 113(1), 108–117.
Résumé: A planar slab of 200 C atoms bound by the Brenner potential is used to study the Langmuir-Hinshelwood (LH) recombination of two physisorbed H atoms on a graphene sheet and to simulate afterward successive collisions of the nascent H-2 molecule with pore walls of a carbonaceous dust grain of the interstellar medium. The study is based on successive propagations of classical trajectories for the 200 C + 2 H atoms. The characteristics of H2 molecules formed by the LH reaction on the flexible surface are found to differ but negligibly from those formed on a rigid one. Collisions of those H,, molecules with graphitic pore walls are studied next. Reflection from and “trapping” onto the surface is observed and discussed. The most important energy transfer is from the molecule vibration to its rotation. This conversion mediates the transfer of the molecule internal energy to its translation or to surface heating. It is found that a single H-2-surface impact has little effect on the internal energy of the molecules. The grain absorbs on the average but a very weak energy. Several impacts are required to appreciably cool the molecule. The molecule cooling is accompanied by a significant increase of its translational energy. The swifter the molecules are or get, the larger the number of their impacts on the surface they undergo per unit time and the more efficiently cooled they get.
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Bachellerie, D., Sizun, M., Aguillon, F., Teillet-Billy, D., Rougeau, N., & Sidis, V. (2009). Unrestricted study of the Eley-Rideal formation of H-2 on graphene using a new multidimensional graphene-H-H potential: role of the substrate. Phys. Chem. Chem. Phys., 11(15), 2715–2729.
Résumé: The Brenner potential is adapted to handle chemical interactions and reactions of H atoms at a graphene surface. The adapted potential reproduces several important features of DFT computed data and reveals an extended puckering of the surface upon its adsorption of an H atom. This potential is used to investigate in a much more realistic way than has been done before, the Eley-Rideal abstraction reaction producing H-2 in H + H-graphene collisions at energies E-col <= 0.2 ev. The graphene surface is represented by a slab of 200 carbon atoms and the study is carried out using classical molecular dynamics for vertical incidences in a cylinder centered about the chemisorption axis. A highlight of the present study is that upon the arrival of the gas phase H atom, the adsorbent C atom is attracted and pulls out its surrounding surface atoms. The hillock thus formed remains puckered until the newly formed molecule is released. The range of impact parameters leading to reaction depends on the collision energy and is governed by the shape of the entrance channel potential; the reaction probability in this range is 100%. On average, in the studied E-col range, the available energy (3.92 eV + E-col) is shared as: 69 52% for the internal energy, 11-23% for the translation energy and 20 25% for the energy imparted the surface. Also, the average vibration and rotation energy levels of the nascent H-2 molecule are, respectively, < v > = 5-4 and < i > = 2-4.
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Morisset, S., Ferro, Y., & Allouche, A. (2009). Isotopic effects in the sticking of H and D atoms on the (0001) graphite surface. CHEMICAL PHYSICS LETTERS, 477(1-3), 225–229.
Résumé: A quantum study of the sticking of hydrogen and deuterium atoms chemisorbed onto graphite (0001) surface is carried out in the collinear scattering approximation, taking into account the phonon modes of the system. The sticking coefficients are calculated for hydrogen and deuterium atoms with incident energies ranging from 0.17 to 0.22 eV, for surface temperatures of 10 and 150 K. The calculation of the sticking coefficients of H and D evidenced an isotopic effect which is discussed. (C) 2009 Elsevier B.V. All rights reserved.
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Nave, S., & Jackson, B. (2009). Methane dissociation on Ni(111) and Pt(111): Energetic and dynamical studies. JOURNAL OF CHEMICAL PHYSICS, 130(5).
Résumé: Electronic structure studies and quantum scattering methods are used to elucidate the differing reactivities of methane on Ni(111) and Pt(111). For both surfaces the lowest energy pathway to dissociation is over the top site, where the static surface barrier to reaction is about 0.14 eV lower on Pt(111) than on Ni(111). If allowed to relax, both surfaces exhibit a puckering of the metal atoms in the vicinity of the adsorbates and at the transition state. Thus, motion of the lattice can change the barrier to reaction. A quantum model for dissociation is employed that includes several molecular coordinates, and allows for coupling to the lattice motion and puckering of the lattice. We find that on Ni(111) the lattice has time to pucker, increasing the reactivity relative to the static surface case. The more massive atoms on the Pt(111) surface do not have time to pucker during the reaction. As both lattices become vibrationally excited the reactivity increases significantly, particularly at low incident energies where tunneling dominates. Our model suggests that tunneling is important for these large barrier systems, particularly at the relatively low incident energies of the experiments. Our work also suggests that at the large nozzle temperatures of the experiments, there are contributions to the total reactivity from vibrationally excited molecules, particularly for Ni(111). Our model is in reasonable agreement with the experimental results for Ni(111), while we significantly underestimate the reactivity on Pt(111) as well as the difference in reactivity between Ni(111) and Pt(111). This may result from errors in our total-energy calculations and/or effects due to motion (tunneling) of the methyl group at the transition state.
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Tiwari, A. K., Nave, S., & Jackson, B. (2009). Methane Dissociation on Ni(111): A New Understanding of the Lattice Effect. PHYSICAL REVIEW LETTERS, 103(25), 253201.
Résumé: The nature of the lattice motion during the dissociation of methane on Ni(111) is analyzed in great detail, and various models for including lattice effects are explored. It is shown that the thermal vibrations of the lattice strongly modify the reactivity, but that the lattice motion is relatively unperturbed by the incident molecule during the collision, in contrast with several earlier predictions. Based on these studies we propose a new model to describe the effects of lattice motion, which agrees well with exact quantum calculations.
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Abouaf, R., & Teillet-Billy, D. (2008). Low energy electron collisions in H2S and H2Se: Structure in dissociative attachment cross-sections. INTERNATIONAL JOURNAL OF MASS SPECTROMETRY, 277(1-3), 79–83.
Résumé: Dissociative electron attachment between 0 and 4 eV has been investigated in hydrogen sulfide and hydrogen selenide with an improved electron resolution (0.040 eV). HS- and HSe- cross-sections versus electron energy present vertical onsets revealing that the potential surfaces of the resonances which are reached around 2 eV are bound. A well-developed and intriguing structure is observed in HS-, S-, HSe- and Se- cross-sections. It could reveal interferences due to an attractive resonance having a lifetime of the order of one vibrational period. The strong similarity between the anion behaviour in H2S and H2Se is in contrast with H2O where no dissociative attachment process occurs in this energy range. (C) 2008 Elsevier B.V. All rights reserved.
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Abouaf, R., Ptasinska, S., & Teillet-Billy, D. (2008). Low energy electron impact on gas phase 5-nitrouracil. CHEMICAL PHYSICS LETTERS, 455(4-6), 169–173.
Résumé: Excitation of the first electronic states, vibrational excitation between 1 and 3 eV, and negative ion formation (0-2 eV) in gas phase 5-nitrouracil are presented. Five singlet states are clearly identified at 4.76; 5.72; 6.82; 7.82 and 9.2 eV. A band at 3.7 eV could be assigned to a triplet state. The vibrational modes observed indicate resonant states having both pi* and sigma* character. The most intense anions (M-NO2) , (M-H) appear at zero energy with huge cross sections (>= 10 18 m(2)). Anion cross sections versus electron energy reveal structures interpreted using the anion energy thresholds found by DFT calculations. (C) 2008 Elsevier B.V. All rights reserved.
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Bergeron, H., Rougeau, N., Sidis, V., Sizun, M., Teillet-Billy, D., & Aguillon, F. (2008). OH Formation from O and H Atoms Physisorbed on a Graphitic Surface through the Langmuir-Hinshelwood Mechanism: A Quasi-Classical Approach. J. Phys. Chem. A, 112(46), 11921–11930.
Résumé: We study the quasi-classical dynamics of OH formation on a graphitic surface through the Langmuir-Hinshelwood (LH) mechanism when both 0 and H ground-state atoms are initially physisorbed on the surface. The model proceeds from previous theoretical work on the LH formation of the H-2 molecule on graphite [Morisset, S.; Aguillon, F.; Sizun, M.; Sidis, V. J. Chem. Phys. 2004, 121, 6493; ibid 2005, 122, 194704]. The H-graphite system is first revisited with a view to get a tractable DFT-GGA computational prescription for the determination of atom physisorption onto graphitic surfaces. The DZP-RPBE combination is found to perform well; it is thereafter used along with MP2 calculations to determine the physisorption characteristics of atomic oxygen on graphitic surfaces. We also deal with chemisorption. In accordance with previous work, we find that 0 chemisorbs on graphite in a singlet spin state epoxy-like conformation. In the triplet state we find only “metastable” chemisorption with an activation barrier of 0.2 eV. The physisorption results are then used in the LH dynamics calculation. We show that in the [0.15 meV, 12 meV] relative collision energy range of the reacting 0 and H atoms on the surface, the OH molecule is produced with a large amount of internal energy (similar or equal to 4 eV) and a significant translation energy (>= 100 meV) relative to the surface.
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Ferro, Y., Teillet-Billy, D., Rougeau, N., Sidis, V., Morisset, S., & Allouche, A. (2008). Stability and magnetism of hydrogen dimers on graphene. PHYSICAL REVIEW B, 78(8), 085417.
Résumé: We report on the magnetism and stability of H dimers on a graphene sheet. Graphene is used as a simple model to grasp the basics of the H interaction with graphitic systems including graphite, graphene, polyaromatic hydrocarbons, and nanotubes. The dimers investigated here are found to be in ferromagnetic, antiferromagnetic, or nonmagnetic states. Results obtained from DFT calculations on the H dimer adsorption are analyzed with the help of spin-density maps. We thereby show that the dimer stability results from the magnetic properties of the pair of H atoms on graphene. The stability of dimers adsorbed in ortho and para positions is particularly emphasized. In order to rationalize the single and double H atom adsorption mechanisms, the whole pair formation process is divided into theoretical elementary steps to which energetic values are assigned.
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Morisset, S., & Allouche, A. (2008). Quantum dynamic of sticking of a H atom on a graphite surface. JOURNAL OF CHEMICAL PHYSICS, 129(2).
Résumé: A quantum study of the sticking of a hydrogen atom chemisorbed onto graphite (0001) surface was carried out also including the phonon modes of the system in the collinear scattering approximation. A new model was developed to extract the substrate vibrational modes from density functional theory (DFT) calculation and include them in the total system dynamics. The resulting coupled-channel equations are numerically developed along time using the wave packet methods. The sticking coefficients are calculated for hydrogen atoms incident energies ranging from 0.17 and 1.3 eV for a surface temperature of 10 K and between 0.17 and 0.2 eV for a surface temperature of 150 K. The results are found to be in good agreement with the experimental work. (C) 2008 American Institute of Physics.
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