Papers by Lars Pettersson
Computer Aided Learning and Instruction in Science and Engineering, 1996
O objetivo do estudo foi avaliar a resiliência em estudantes do Ensino Médio e sua associação com... more O objetivo do estudo foi avaliar a resiliência em estudantes do Ensino Médio e sua associação com variáveis sociodemográficas e contribuição da escola em seu desenvolvimento pessoal. A amostra foi composta de 140 alunos de uma Escola Estadual de uma cidade da região metropolitana de Porto Alegre. Foram utilizados, como instrumentos de pesquisa, um questionário para levantamento de variáveis demográficas e sociais e a Escala de Resiliência, adaptada por Pesce, Assis, Avanci, Santos, Malaquias e Carvalhaes (2005), que constitui-se de três dimensões: Independência e determinação; Resolução de ações e valores; Autoconfiança e Capacidade de adaptação a situações. Resultados indicam associação negativa entre renda familiar e a dimensão de resiliência de Independência e determinação. Associação positiva foi identificada entre a percepção de que a escola contribui para o desenvolvimento pessoal e a dimensão de Resolução de ações e valores.
Theoretical Modelling of Chemisorption and Reactions on Metal-Oxide Surfaces
Chemisorption and Reactivity on Supported Clusters and Thin Films, 1997
... For polar surfaces, which undergo reconstruction, the effects are larger and must be consider... more ... For polar surfaces, which undergo reconstruction, the effects are larger and must be considered. As an example we discuss the Cu+ terminated polar (100) surface of Cu20 [23 ... with a lattice parameter of 4.267 A [24]; the lattice parameter resulting from the simulation was 4.270 ...
The journal of physical chemistry. B, Jan 2, 2018
The structure factor and oxygen-oxygen pair-distribution functions of amorphous ices at liquid ni... more The structure factor and oxygen-oxygen pair-distribution functions of amorphous ices at liquid nitrogen temperature ( T = 77 K) have been derived from wide-angle X-ray scattering (WAXS) up to interatomic distances of r = 23 Å, where local structure differences between the amorphous ices can be seen for the entire range. The distances to the first coordination shell for low-, high-, and very-high-density amorphous ice (LDA, HDA, VHDA) were determined to be 2.75, 2.78, and 2.80 Å, respectively, with high accuracy due to measurements up to a large momentum transfer of 23 Å. Similarities in pair-distribution functions between LDA and supercooled water at 254.1 K, HDA and liquid water at 365.9 K, and VHDA and high-pressure liquid water were found up to around 8 Å, but beyond that at longer distances, the similarities were lost. In addition, the structure of the high-density amorphous ices was compared to high-pressure crystalline ices IV, IX , and XII, and conclusions were drawn about th...
Gas-phase hydrogen abstraction from methane using metal oxides. Theoretical study
The Journal of Physical Chemistry, 1991
Page 1. 3214 J. Phys. Chem. 1991, 95, 3214-3217 dP/dt -NTkdP (8) the basis of other experiments, ... more Page 1. 3214 J. Phys. Chem. 1991, 95, 3214-3217 dP/dt -NTkdP (8) the basis of other experiments, as discussed above. Acknowledgment. This research was supported by the Research Gorp, with matching funds from the University of California, ...
Hydrogen abstraction from methane on a magnesia (001) surface
The Journal of Physical Chemistry, 1991
Page 1. J. Phys. Chem. 1991,95,7401-7405 7401 Hydrogen Abstraction from Methane on an UgO(OO1) Su... more Page 1. J. Phys. Chem. 1991,95,7401-7405 7401 Hydrogen Abstraction from Methane on an UgO(OO1) Surface but J. B0net and Lars G. M. Pettenson* Institute of Theoretical Physics, University of Stockholm, Vanadisvdgen ...
Journal of Non-Crystalline Solids, 2015
Here we discuss the structure of water in terms of a temperature-dependent balance between two cl... more Here we discuss the structure of water in terms of a temperature-dependent balance between two classes of hydrogen-bonded structures. At high and down to mildly supercooled temperatures most molecules favor a closer packing than tetrahedral, with strongly distorted hydrogen bonds. This allows the quantized librational modes to be excited and contribute to the entropy while the loss of enthalpy due to breaking hydrogen bonds is compensated by enhanced van der Waals interactions. Tetrahedral hydrogen bonding is of lower enthalpy resulting in tetrahedrally bonded water patches appearing, but only as fluctuations with size and life-time increasing at lower temperatures. Measurements of the structure at deeply supercooled conditions show a continuous increase in tetrahedrality which becomes accelerated below the temperature of homogeneous ice nucleation. The two local structures are connected to the liquid-liquid critical point (LLCP) hypothesis in supercooled water and correspond to high density liquid (HDL) and low density liquid (LDL). We propose that both HDL and LDL behave as normal liquids and that the anomalous properties of water result from the transition between them, which occurs over a wide temperature range at ambient pressure. The key issue is the competition between incompatible conditions for maximizing the entropy, favored in HDL, and minimizing the enthalpy, favored in LDL, which leads to the instability in the liquid and is the fundamental origin of the proposed LLCP.
Physical Review Letters, 2017
Proceedings of the National Academy of Sciences of the United States of America, Aug 1, 2017
Water exists in high- and low-density amorphous ice forms (HDA and LDA), which could correspond t... more Water exists in high- and low-density amorphous ice forms (HDA and LDA), which could correspond to the glassy states of high- (HDL) and low-density liquid (LDL) in the metastable part of the phase diagram. However, the nature of both the glass transition and the high-to-low-density transition are debated and new experimental evidence is needed. Here we combine wide-angle X-ray scattering (WAXS) with X-ray photon-correlation spectroscopy (XPCS) in the small-angle X-ray scattering (SAXS) geometry to probe both the structural and dynamical properties during the high-to-low-density transition in amorphous ice at 1 bar. By analyzing the structure factor and the radial distribution function, the coexistence of two structurally distinct domains is observed at T = 125 K. XPCS probes the dynamics in momentum space, which in the SAXS geometry reflects structural relaxation on the nanometer length scale. The dynamics of HDA are characterized by a slow component with a large time constant, aris...
The journal of physical chemistry letters, Jan 5, 2017
Copper electrocatalysts derived from an oxide have shown extraordinary electrochemical properties... more Copper electrocatalysts derived from an oxide have shown extraordinary electrochemical properties for the carbon dioxide reduction reaction (CO2RR). Using in situ ambient pressure X-ray photoelectron spectroscopy and quasi in situ electron energy-loss spectroscopy in a transmission electron microscope, we show that there is a substantial amount of residual oxygen in nanostructured, oxide-derived copper electrocatalysts but no residual copper oxide. On the basis of these findings in combination with density functional theory simulations, we propose that residual subsurface oxygen changes the electronic structure of the catalyst and creates sites with higher carbon monoxide binding energy. If such sites are stable under the strongly reducing conditions found in CO2RR, these findings would explain the high efficiencies of oxide-derived copper in reducing carbon dioxide to multicarbon compounds such as ethylene.
The journal of physical chemistry letters, Jan 2, 2016
The concept of bonding and antibonding orbitals is fundamental in chemistry. The population of th... more The concept of bonding and antibonding orbitals is fundamental in chemistry. The population of those orbitals and the energetic difference between the two reflect the strength of the bonding interaction. Weakening the bond is expected to reduce this energetic splitting, but the transient character of bond-activation has so far prohibited direct experimental access. Here we apply time-resolved soft X-ray spectroscopy at a free-electron laser to directly observe the decreased bonding-antibonding splitting following bond-activation using an ultrashort optical laser pulse.
The Journal of chemical physics, Jan 28, 2016
We analyze the recent temperature dependent oxygen-oxygen pair-distribution functions from experi... more We analyze the recent temperature dependent oxygen-oxygen pair-distribution functions from experimental high-precision x-ray diffraction data of bulk water by Skinner et al. [J. Chem. Phys. 141, 214507 (2014)] with particular focus on the intermediate range where small, but significant, correlations are found out to 17 Å. The second peak in the pair-distribution function at 4.5 Å is connected to tetrahedral coordination and was shown by Skinner et al. to change behavior with temperature below the temperature of minimum isothermal compressibility. Here we show that this is associated also with a peak growing at 11 Å which strongly indicates a collective character of fluctuations leading to the enhanced compressibility at lower temperatures. We note that the peak at ∼13.2 Å exhibits a temperature dependence similar to that of the density with a maximum close to 277 K or 4 °C. We analyze simulations of the TIP4P/2005 water model in the same manner and find excellent agreement between s...
Chemical reviews, Jan 13, 2016
Detection of adsorbate overlayer structural transitions using sum-frequency generation spectroscopy
Surface Science, 2015
We demonstrate that temperature-programmed vibrational sum-frequency generation (SFG) spectroscop... more We demonstrate that temperature-programmed vibrational sum-frequency generation (SFG) spectroscopy has a unique sensitivity to certain adsorbate overlayer structural transitions. In the CO stretchi ...
Chemical reviews, Jul 13, 2016
Water is the most abundant liquid on earth and also the substance with the largest number of anom... more Water is the most abundant liquid on earth and also the substance with the largest number of anomalies in its properties. It is a prerequisite for life and as such a most important subject of current research in chemical physics and physical chemistry. In spite of its simplicity as a liquid, it has an enormously rich phase diagram where different types of ices, amorphous phases, and anomalies disclose a path that points to unique thermodynamics of its supercooled liquid state that still hides many unraveled secrets. In this review we describe the behavior of water in the regime from ambient conditions to the deeply supercooled region. The review describes simulations and experiments on this anomalous liquid. Several scenarios have been proposed to explain the anomalous properties that become strongly enhanced in the supercooled region. Among those, the second critical-point scenario has been investigated extensively, and at present most experimental evidence point to this scenario. ...
Theoretical potential curves for the A2II and X2Σ+ states of NO2+ and an experimental search for the A-X transition
Chemical Physics Letters, 1992
Experimental and theoretical characterization of the structure of defects at the pyrite FeS(2)(100) surface
X-ray and Electron Spectroscopy of Water
Chemical reviews, Jul 31, 2016
Here we present an overview of recent developments of X-ray and electron spectroscopy to probe wa... more Here we present an overview of recent developments of X-ray and electron spectroscopy to probe water at different temperatures. Photon-induced ionization followed by detection of electrons from either the O 1s level or the valence band is the basis of photoelectron spectroscopy. Excitation between the O 1s and the unoccupied states or occupied states is utilized in X-ray absorption and X-ray emission spectroscopies. These techniques probe the electronic structure of the liquid phase and show sensitivity to the local hydrogen-bonding structure. Both experimental aspects related to the measurements and theoretical simulations to assist in the interpretation are discussed in detail. Different model systems are presented such as the different bulk phases of ice and various adsorbed monolayer structures on metal surfaces.
Structure of water adsorbed on Cu(110): H-up, H-down, or both?
Chemical Physics Letters, 2006
On the character of the O22+ A 3Σu+ state
The Journal of Chemical Physics, 1991
The Journal of chemical physics, Jan 28, 2016
In the present study, we investigate the process of evaporative cooling of nanometer-sized drople... more In the present study, we investigate the process of evaporative cooling of nanometer-sized droplets in vacuum using molecular dynamics simulations with the TIP4P/2005 water model. The results are compared to the temperature evolution calculated from the Knudsen theory of evaporation which is derived from kinetic gas theory. The calculated and simulation results are found to be in very good agreement for an evaporation coefficient equal to unity. Our results are of interest to experiments utilizing droplet dispensers as well as to cloud micro-physics.
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Papers by Lars Pettersson