Six-dimensional theoretical study of H2 scattering from LiF(001): From thermal to high incidence energies

We have computed an accurate potential energy surface (PES) describing the electronic structure of the system H2/LiF(001). Based on this PES, we have performed an analysis of the dynamics of the system trying to understand recent experimental results obtained at fast grazing incidence condition

Scattering of atoms and diatomic molecules from non-metal surfaces

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química. Fecha de lectura: 27 de mayo de 201

Theoretical study of noble gases diffraction from Ru(0001) using van der Waals DFT-based potentials

This study aims to analyze the role of van der Waals forces in the diffraction process of noble gases from a metal surface. We made use of different vdW implementations to rationalize the effect of dispersion forces on the corrugation of the system, the resulting scattering patterns and on the eventual diffraction result

Vibrational dynamics of CO on Pd(111) in and out of thermal equilibrium

Using many-body perturbation theory and density functional perturbation theory, we study the vibrational spectra of the internal stretch (IS) mode of CO on Pd(111) for the bridge and hollow adsorption structures that are experimentally identified at 0.5~ML coverage. Our theoretical treatment allows us to determine the temperature dependence of the IS vibrational spectra under thermal conditions as well as the time evolution of the non-equilibrium transient spectra induced by femtosecond laser pulses. Under thermal conditions (i.e., for equal electronic $T_e$ and phononic $T_l$ temperatures), the calculated lifetimes at 10-150~K are mostly due to nonadiabatic couplings (NC), i.e., first-order electronic excitations. As temperature increases, also the contribution of the second-order electron mediated phonon-phonon couplings (EMPPC) progressively increases from 25\% at low temperatures to 50\% at 300~K. Our calculations for the laser-induced non-equilibrium conditions comprise experimental absorbed fluences of 6-130~J/m$^2$. For fluences for which $T_e>$2000~K, the transient vibrational spectra are characterized by two different regimes that follow the distinct time-evolution of $T_e$ and $T_l$ and are respectively dominated by NC and EMPPC processes. At lower fluences, the initial fast regime becomes progressively negligible as $T_e$ decreases and only the steady second regime remains visible. Qualitatively, all these spectral properties are common to the both adsorption structures studied here.Comment: 16 pages, 10 figures, 3 table

Anomalous transient blueshift in the internal stretch mode of CO/Pd(111)

In time-resolved pump-probe vibrational spectroscopy the internal stretch mode of polar molecules is utilized as a key observable to characterize the ultrafast dynamics of adsorbates on surfaces. The adsorbates non-adiabatic intermode couplings are the commonly accepted mechanisms behind the observed transient frequency shifts. Here, we study the CO/Pd(111) system with a robust theoretical framework that includes electron-hole pair excitations and electron-mediated coupling between the vibrational modes. A mechanism is revealed that screens the electron-phonon interaction and originates a blueshift under ultrafast non-equilibrium conditions. The results are explained in terms of the abrupt change in the density of states around the Fermi level, and are instrumental for understanding dynamics at multi-component surfaces involving localized and standard $s$ or $p$ states.Comment: 3 figures, 5 page

Vibrational deexcitation and rotational excitation of H2 and D2 scattered from Cu(111): Adiabatic versus non-adiabatic dynamics

The following article appeared in Journal of Chemical Physic 137.6 (2012): 064707 and may be found at http://scitation.aip.org/content/aip/journal/jcp/137/6/10.1063/1.4742907We have studied survival and rotational excitation probabilities of H2(vi = 1, Ji = 1) and D2(vi = 1, Ji = 2) upon scattering from Cu(111) using six-dimensional (6D) adiabatic (quantum and quasi-classical) and non-adiabatic (quasi-classical) dynamics. Non-adiabatic dynamics, based on a friction model, has been used to analyze the role of electron-hole pair excitations. Comparison between adiabatic and non-adiabatic calculations reveals a smaller influence of non-adiabatic effects on the energy dependence of the vibrational deexcitation mechanism than previously suggested by low-dimensional dynamics calculations. Specifically, we show that 6D adiabatic dynamics can account for the increase of vibrational deexcitation as a function of the incidence energy, as well as for the isotope effect observed experimentally in the energy dependence for H2(D2)/Cu(100). Furthermore, a detailed analysis, based on classical trajectories, reveals that in trajectories leading to vibrational deexcitation, the minimum classical turning point is close to the top site, reflecting the multidimensionally of this mechanism. On this site, the reaction path curvature favors vibrational inelastic scattering. Finally, we show that the probability for a molecule to get close to the top site is higher for H2 than for D2, which explains the isotope effect found experimentallyThis work has been financially supported by the DGI (Project Nos. FIS2010-15127 and FIS2010-19609-C02-02), the CAM (Project No. 2009/MAT1726), the Basque Dpto. de Educación, Universidades e Investigación, and the UPV/EHU (Project No. IT-366-07

Experimental and theoretical study of rotationally inelastic diffraction of H_2(D_2) from methyl-terminated Si(111)

Fundamental details concerning the interaction between H_2 and CH_3–Si(111) have been elucidated by the combination of diffractive scattering experiments and electronic structure and scattering calculations. Rotationally inelastic diffraction (RID) of H_2 and D_2 from this model hydrocarbon-decorated semiconductor interface has been confirmed for the first time via both time-of-flight and diffraction measurements, with modest j = 0 → 2 RID intensities for H_2 compared to the strong RID features observed for D_2 over a large range of kinematic scattering conditions along two high-symmetry azimuthal directions. The Debye-Waller model was applied to the thermal attenuation of diffraction peaks, allowing for precise determination of the RID probabilities by accounting for incoherent motion of the CH_3–Si(111) surface atoms. The probabilities of rotationally inelastic diffraction of H_2 and D_2 have been quantitatively evaluated as a function of beam energy and scattering angle, and have been compared with complementary electronic structure and scattering calculations to provide insight into the interaction potential between H_2 (D_2) and hence the surface charge density distribution. Specifically, a six-dimensional potential energy surface (PES), describing the electronic structure of the H_2(D_2)/CH_3−Si(111) system, has been computed based on interpolation of density functional theory energies. Quantum and classical dynamics simulations have allowed for an assessment of the accuracy of the PES, and subsequently for identification of the features of the PES that serve as classical turning points. A close scrutiny of the PES reveals the highly anisotropic character of the interaction potential at these turning points. This combination of experiment and theory provides new and important details about the interaction of H_2 with a hybrid organic-semiconductor interface, which can be used to further investigate energy flow in technologically relevant systems

Experimental and theoretical study of rotationally inelastic diffraction of H_2(D_2) from methyl-terminated Si(111)

Fundamental details concerning the interaction between H_2 and CH_3–Si(111) have been elucidated by the combination of diffractive scattering experiments and electronic structure and scattering calculations. Rotationally inelastic diffraction (RID) of H_2 and D_2 from this model hydrocarbon-decorated semiconductor interface has been confirmed for the first time via both time-of-flight and diffraction measurements, with modest j = 0 → 2 RID intensities for H_2 compared to the strong RID features observed for D_2 over a large range of kinematic scattering conditions along two high-symmetry azimuthal directions. The Debye-Waller model was applied to the thermal attenuation of diffraction peaks, allowing for precise determination of the RID probabilities by accounting for incoherent motion of the CH_3–Si(111) surface atoms. The probabilities of rotationally inelastic diffraction of H_2 and D_2 have been quantitatively evaluated as a function of beam energy and scattering angle, and have been compared with complementary electronic structure and scattering calculations to provide insight into the interaction potential between H_2 (D_2) and hence the surface charge density distribution. Specifically, a six-dimensional potential energy surface (PES), describing the electronic structure of the H_2(D_2)/CH_3−Si(111) system, has been computed based on interpolation of density functional theory energies. Quantum and classical dynamics simulations have allowed for an assessment of the accuracy of the PES, and subsequently for identification of the features of the PES that serve as classical turning points. A close scrutiny of the PES reveals the highly anisotropic character of the interaction potential at these turning points. This combination of experiment and theory provides new and important details about the interaction of H_2 with a hybrid organic-semiconductor interface, which can be used to further investigate energy flow in technologically relevant systems

Disentangling the geologic, human and climate drivers influencing sediment deposition in volcanic lakes on the Azores Archipelago

IAL-IPA joint meeting "Lakes as Memories of the Landscape", Patagonia, Argentina, 27 November-01 December 2022The Azores Archipelago Western (AAWG) and Central (AACG) groups present a high diversity of tectono-volcanic settings, and, therefore, a wide range of lake-watershed system morphometries. This archipelago has suffered from anthropic impacts, mainly abrupt land-use changes, since medieval times (between 700 and 850 CE), and increasingly after the Portuguese arrival in the 15th century. In this complex geologic and human context, we used a multiproxy approach in sediment records from Lakes Caldeirão (Corvo Island), Funda (Flores Island), and Caveiro (Pico Island) to demonstrate a complex interlinking among several environmental drivers over the last millennia. Paleoenvironmental changes have been defined by a multivariate analysis of sedimentary facies, biogeochemical and mineralogical data. This analysis highlights that the most prominent sedimentary process in the AAWG lakes (Caldeirao and Funda) is hydrological grain size sorting, driven by runoff. Additionally, smooth catchment slopes of the low-gradient lake, Caldeirão, modulated this process by favouring rock grain size diminution through weathering, whereas the steep topographic-bathymetric profile of the high-gradient lake, Funda, do through water-level fluctuations. The frequent volcanic activity of the AACG and the small size of Caveiro lake catchment favoured the deposit of pyroclastic tephra through direct fallout in the lake, over the catchment-sourced inputs, reworked by climate and tectonic activity. The biogeochemical and mineral composition of the sedimentary records present extreme change rates at 1288+28-22-1388+41-32 CE, corresponding with the age of the most intense landscape transformation. Therefore, to obtain robust climate reconstructions from these Azorean lacustrine records, we present a detailed statistical approach to isolate the climate signal from volcano-tectonic, morphometric, and anthropic driversThis research was funded by the Spanish Ministry of Economy and Competitiveness research projects PaleoNAO (CGL2010-15767), RapidNAO (CGL2013-40608-R), PaleoModes (CGL2016-75281-C2), and NEOCLIM (PID2020-113798GB-C33), and through Portuguese Science Foundation (FCT) (DL57/2016/ICETA/EEC2018/25) and the DISCOVERAZORES (PTDC/CTA-AMB/28511/2017)N

The role of the initial ro-vibrational state in molecule/surface scattering under fast grazing incidence

We have studied diffractive scattering of H2 from LiF(100) under fast grazing incidence, as a function of the initial ro-vibrational state of the molecule. We show that diffraction patterns, i.e., the relative diffraction peaks intensity, vary significantly with the initial ro-vibrational state. This result indicates that in order to perform accurate comparisons between experimental and theoretical results, some knowledge about the initial ro-vibrational distribution of the molecular experimental beam is required. We hope that this result will encourage experimental groups working on the field to design and develop the techniques required to provide such informationMICINN FIS2013-42002-