scholarly journals Segregation effect and N2 binding energy reduction in CO-N2 systems adsorbed on water ice substrates

2018 ◽  
Vol 619 ◽  
pp. A111 ◽  
Author(s):  
T. Nguyen ◽  
S. Baouche ◽  
E. Congiu ◽  
S. Diana ◽  
L. Pagani ◽  
...  
Keyword(s):  
Binding Energy ◽  
Gas Phase ◽  
Adsorption Energy ◽  
High Vacuum ◽  
Amorphous Solid ◽  
Abundant Species ◽  
Binding Energies ◽  
Ultra High Vacuum ◽  
Pure Species ◽  
Water Ice

Context. CO and N2 are two abundant species in molecular clouds. CO molecules are heavily depleted from the gas phase towards the centre of pre-stellar cores, whereas N2 maintains a high gas phase abundance. For example, in the molecular cloud L183, CO is depleted by a factor of ≈400 in its centre with respect to the outer regions of the cloud, whereas N2 is only depleted by a factor of ≈20. The reason for this difference is not yet clear, since CO and N2 have identical masses, similar sticking properties, and a relatively close energy of adsorption. Aims. We present a study of the CO-N2 system in sub-monolayer regimes, with the aim to measure, analyse and elucidate how the adsorption energy of the two species varies with coverage, with much attention to the case where CO is more abundant than N2. Methods. Experiments were carried out using the ultra-high vacuum (UHV) set-up called VENUS. Sub-monolayers of either pure 13CO or pure 15N2 and 13CO:15N2 mixtures were deposited on compact amorphous solid water ice, and crystalline water ice. Temperature-programmed desorption experiments, monitored by mass spectrometry, are used to analyse the distributions of binding energies of 13CO and 15N2 when adsorbed together in different proportions. Results. The distribution of binding energies of pure species varies from 990 K to 1630 K for 13CO, and from 890 K to 1430 K for 15N2. When a CO:N2 mixture is deposited, the 15N2 binding energy distribution is strongly affected by the presence of 13CO, whereas the adsorption energy of CO is unaltered. Conclusions. Whatever types of water ice substrate we used, the N2 effective binding energy was significantly lowered by the presence of CO molecules. We discuss the possible impact of this finding in the context of pre-stellar cores.

scholarly journals Implications of Ice Morphology for Comet Formation

2005 ◽  
Vol 13 ◽  
pp. 491-494 ◽  
Author(s):  
M. P. Collings ◽  
J. W. Dever ◽  
M. R. S. McCoustra ◽  
H. J. Fraser
Keyword(s):  
Surface Science ◽  
High Vacuum ◽  
Binding Energies ◽  
Ultra High Vacuum ◽  
Water Ice ◽  
Reflection Absorption Infrared Spectroscopy ◽  
Thermodynamic Conditions ◽  
Temperature Programmed ◽  
Additional Constraints ◽  
Ice Morphology

AbstractLaboratory surface science under ultra-high vacuum (UHV) conditions allows us to simulate the growth of ices in astrophysical environments. Using the techniques of temperature programmed desorption (TPD), reflection-absorption infrared spectroscopy (RAIRS) and micro-balance methods, we have studied binary ice systems consisting of water (H2O) and variety of other species including carbon monoxide (CO), at astrophysically relevant conditions of temperature and pressure. We present results that demonstrate that the morphology of water ice has an important influence on the behavior of such systems, by allowing processes such as diffusion and trapping that can not be understood through a knowledge of the binding energies of the species alone. Through an understanding of the implications of water ice morphology on the behavior of ice mixtures in the interstellar environment, additional constraints can be placed on the thermodynamic conditions and ice compositions during comet formation.

Xps and Voltammetry Studies of Redox Behavior of Lacrl1− NixO3 Electrodes

1998 ◽  
Vol 548 ◽  
Author(s):  
Greg Vovk ◽  
Xiaohua Chen ◽  
Charles A. Mims
Keyword(s):  
Redox State ◽  
Electrochemical Cell ◽  
High Vacuum ◽  
Adsorption Properties ◽  
Binding Energies ◽  
Redox Properties ◽  
Ultra High Vacuum ◽  
Redox Behavior ◽  
Heated Sample

ABSTRACTAn in-situ XPS and voltammetry investigation of the redox properties of LaCrj1-xNixO3(x = 0.4, 1) was carried out by incorporating the materials as one electrode in an electrochemical cell (LaCr1xNixO3|YSZ|Pd:PdO), which was directly mounted on a heated sample stage in an ultra high vacuum (UHV) chamber. Under a 0.7V cathodic bias, the perovskites reduce from formal oxidation state of Ni3+ to Ni2+. This reduction is accompanied by wholesale shifts of the Cr and O core level binding energies, in keeping with the delocalized electronic states in the material. The adsorption properties of the surfaces are affected by the redox state of the surfaces; increased CO2adsorption is observed on the reduced (and therefore more basic) surface.

Probing Intramolecular Interaction of Stereoisomers Using Computational Spectroscopy

2020 ◽  
Vol 73 (8) ◽  
pp. 813
Author(s):  
Feng Wang ◽  
Shawkat Islam ◽  
Frederick Backler
Keyword(s):  
Hydrogen Bonding ◽  
Binding Energy ◽  
Gas Phase ◽  
Intramolecular Interaction ◽  
Dipole Moments ◽  
Energy Difference ◽  
Binding Energies ◽  
Intramolecular Interactions ◽  
Computational Spectroscopy ◽  
Ionic States

Several model stereoisomers such as ferrocene (Fc), methoxyphenol, and furfural conformers are discussed. It was discovered that the Fc IR spectroscopic band(s) below 500cm−1 serve as fingerprints for eclipsed (splitting 17 (471–488)cm−1) and staggered Fc (splitting is ~2 (459–461)cm−1) in the gas phase. It is revealed that in the gas phase the dominance of the eclipsed Fc (D5h) at very low temperatures changes to a mixture of both eclipsed and staggered Fc when the temperature increases. However, in solvents such as CCl4, eclipsed Fc dominates at room temperature (300K) due to the additional solvation energy. Intramolecular interactions of organic model compounds such as methoxyphenols (guaiacol (GUA) and mequinol (MEQ)) and furfural, ionization energies such as the carbon 1s (core C1s), as well as valence binding energy spectra serve this purpose well. Hydrogen bonding alters the C1s binding energies of the methoxy carbon (C(7)) of anti-syn and anti-gauche conformers of GUA to 292.65 and 291.91eV, respectively. The trans and cis MEQ conformers, on the other hand, are nearly energy degenerate, whereas their dipole moments are significantly different: 2.66 Debye for cis and 0.63 Debye for trans-MEQ. Moreover, it is found that rotation around the Cring–OH and the Cring–OCH3 bonds differ in energy barrier height by ~0.50 kcal⋅mol−1. The Dyson orbital momentum profiles of the most different ionic states, 25a′ (0.35eV) and 3a′ (−0.33eV), between cis and trans-MEQ in outer valence space (which is measurable using electron momentum spectroscopy (EMS)), exhibit quantitative differences. Finally, the molecular switch from trans and cis-furfural engages with a small energy difference of 0.74 kcal mol−1, however, at the calculated C(3)(–H⋅⋅⋅O=C) site the C1s binding energy difference is 0.105eV (2.42 kcal mol−1) and the NMR chemical shift of the same carbon site is also significant; 7.58ppm from cis-furfural without hydrogen bonding.

CORRELATION AMONG THE ELECTRONIC STATE IN Sn-DOPED YBCO SYSTEM

1991 ◽  
Vol 05 (08) ◽  
pp. 581-585
Author(s):  
H. ZHANG ◽  
S.Q. FENG ◽  
Q.R. FENG ◽  
X. ZHU
Keyword(s):  
Content Analysis ◽  
Binding Energy ◽  
Photoelectron Spectroscopy ◽  
Strong Correlation ◽  
Single Phase ◽  
Vacuum Chamber ◽  
High Vacuum ◽  
Electronic States ◽  
Ultra High Vacuum ◽  
X Ray

We have performed an X-ray photoelectron spectroscopy investigation on single-phase samples of Sn -doped YBCO system, together with structure analysis, oxygen content analysis, and superconductivity measurements. The experiment gave evidence that there is a strong correlation between the electronic states of copper and oxygen. When the sample was heated to 600°C for 20 minutes in vacuum chamber, the oxygen escaped from the sample, the binding energy of Cu 2p was decreased, and the two indistinct components of O 1s became clear. Keeping the sample in ultra-high vacuum for 24 hours, a similar result was obtained.

XPS and AES Study of Oxygen Interaction on the Surface of the ZrNi Intermetallic Compound

2012 ◽  
Vol 445 ◽  
pp. 709-713 ◽  
Author(s):  
A. Roustila ◽  
A. Rabehi ◽  
M. Souici ◽  
J. Chene
Keyword(s):  
Intermetallic Compound ◽  
Photoelectron Spectroscopy ◽  
High Vacuum ◽  
Chemical Properties ◽  
Binding Energies ◽  
Ultra High Vacuum ◽  
Ion Sputtering ◽  
Xps Spectra ◽  
Preferential Sputtering ◽  
Application Fields

ZrNi intermetallic compound is used in several application fields due to its very favorable characteristics for the storage of hydrogen. The hydrogen reactions are important, it is vital to examine the evolution of physico-chemical properties at the surface. X-ray photoelectron spectroscopy, is used to follow the evolution of electronic properties of ZrNi versus the ion sputtering in ultra high vacuum in the range 300-600°C. Morever, the evolution of species concentrations at the surface of ZrNi in the range 100-700°C is followed by means of Auger electron spectroscopy. The present results show that temperature and ion sputtering favor significant changes in surface properties of ZrNi. In situ annealing of ZrNi favors the oxygen decontamination associated with segregation of zirconium metal on the surface. The values of binding energies deduced from the reconstruction of XPS spectra, allowed the identification of species present at the surface. The results indicate that nickel is not contaminated and all the obtained sub-oxides are related to bonding states of oxygen with zirconium (Zr2O, ZrO, ZrO2and Zr2O3). The ion sputtering of the surface of ZrNi causes preferential sputtering phenomenon. The later results from the removal of surface layers and from the appearance of zirconium oxide layers initially present on the surface. The results obtained by AES show the segregation of impurities (oxygen and carbon) and of zirconium on the surface of ZrNi. AES observations of Zr segregation start to be important above 300°C and this is in agreement with XPS analysis showing a Zr enrichment of the surface of ZrNi.

scholarly journals Geometries, Reactivity and Binding Energy of Urea on Mg9O9

2020 ◽  
Vol 5 (3) ◽  
Author(s):  
Antonio Luiz Almeida ◽  
João Batista Lopes Martins
Keyword(s):  
Binding Energy ◽  
Gas Phase ◽  
Chemical Potential ◽  
Function Analysis ◽  
Binding Energies ◽  
Chemical Hardness ◽  
Atomic Charges ◽  
Quantum Chemical Descriptors ◽  
Site Selectivity ◽  
Global And Local

In this paper we present global and local reactivity results of the urea gas phase molecule and gas phase (MgO)18 agglomerated for understand charge distribution and binding energy (MgO)-UREA. We analyze the quantum chemical descriptors, ionization potential (I), electron affinity (A), chemical hardness (ɳ), chemical potential (μ) and Global Philicity Index (ω) and site reactivity or site selectivity condensed Fukui function analysis of the distribution of atomic charges investigated with  methods of Mulliken, Merz-Kolman and Natural Atomic Charges. For instance, the binding energies of MgO-Urea systems are.

scholarly journals Variation of the sticking of methanol on low-temperature surfaces as a possible obstacle to freeze out in dark clouds

2020 ◽  
Vol 494 (3) ◽  
pp. 4119-4129
Author(s):  
K A K Gadallah ◽  
A Sow ◽  
E Congiu ◽  
S Baouche ◽  
F Dulieu
Keyword(s):  
Low Temperature ◽  
Surface Temperature ◽  
Gas Phase ◽  
Amorphous Solid ◽  
Vacuum System ◽  
Initial Value ◽  
Water Ice ◽  
Dark Clouds ◽  
Reflection Absorption Infrared Spectroscopy ◽  
Temperature Programmed

ABSTRACT Sticking of gas-phase methanol on different cold surfaces – gold, 13CO, and amorphous solid water (ASW) ice – was studied as a function of surface temperature (7–40 K). In an ultrahigh-vacuum system, reflection absorption infrared spectroscopy (RAIRS) and temperature-programmed desorption methods were simultaneously used to measure methanol sticking efficiency. Methanol band strengths obtained by RAIRS vary greatly depending on the type of the surface. Nevertheless, both methods indicate that the sticking of methanol on different surfaces varies with surface temperature. The sticking efficiency decreases by 30${{\ \rm per\ cent}}$ as the surface temperature goes from 7 to 16 K, then gradually increases until the temperature is 40 K, reaching approximately the initial value found at 7 K. The sticking of methanol differs slightly from one surface to another. At low temperature, it has the lowest values on gold, intermediate values on water ice, and the highest values are found on CO ice, although these differences are smaller than those observed with temperature variation. There exists probably a turning point during the structural organization of methanol ice at 16 K, which makes the capture of methanol from the gas phase less efficient. We wonder if this observation could explain the surprising high abundance of gaseous methanol observed in dense interstellar cores, where it should accrete on grains. In this regard, a 30${{\ \rm per\ cent}}$ reduction of the sticking is not sufficient in itself but transposed to astrophysical conditions dominated by cold gas (∼15 K), which could reduce the sticking efficiency by two orders of magnitude.

Fluorescence resonance energy transfer of gas-phase ions under ultra high vacuum and ambient conditions

2014 ◽  
Vol 16 (19) ◽  
pp. 8911-8920 ◽  
Author(s):  
Vladimir Frankevich ◽  
Vitaliy Chagovets ◽  
Fanny Widjaja ◽  
Konstantin Barylyuk ◽  
Zhiyi Yang ◽  
...  
Keyword(s):  
Energy Transfer ◽  
Gas Phase ◽  
Fluorescence Resonance Energy Transfer ◽  
High Vacuum ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Ultra High Vacuum ◽  
Ambient Conditions ◽  
Gas Phase Ions ◽  
Fluorescence Resonance

scholarly journals Methanol ice co-desorption as a mechanism to explain cold methanol in the gas-phase

2018 ◽  
Vol 612 ◽  
pp. A88 ◽  
Author(s):  
N. F. W. Ligterink ◽  
C. Walsh ◽  
R. G. Bhuin ◽  
S. Vissapragada ◽  
J. Terwisscha van Scheltinga ◽  
...  
Keyword(s):  
Gas Phase ◽  
Thermal Desorption ◽  
High Vacuum ◽  
Protoplanetary Disk ◽  
Ultra High Vacuum ◽  
Indirect Pathway ◽  
Cold Environments ◽  
Chemical Modelling ◽  
Phase Chemistry ◽  
The Impact

Context. Methanol is formed via surface reactions on icy dust grains. Methanol is also detected in the gas-phase at temperatures below its thermal desorption temperature and at levels higher than can be explained by pure gas-phase chemistry. The process that controls the transition from solid state to gas-phase methanol in cold environments is not understood. Aims. The goal of this work is to investigate whether thermal CO desorption provides an indirect pathway for methanol to co-desorb at low temperatures. Methods. Mixed CH3OH:CO/CH4 ices were heated under ultra-high vacuum conditions and ice contents are traced using RAIRS (reflection absorption IR spectroscopy), while desorbing species were detected mass spectrometrically. An updated gas-grain chemical network was used to test the impact of the results of these experiments. The physical model used is applicable for TW Hya, a protoplanetary disk in which cold gas-phase methanol has recently been detected. Results. Methanol release together with thermal CO desorption is found to be an ineffective process in the experiments, resulting in an upper limit of ≤ 7.3 × 10−7 CH3OH molecules per CO molecule over all ice mixtures considered. Chemical modelling based on the upper limits shows that co-desorption rates as low as 10−6 CH3OH molecules per CO molecule are high enough to release substantial amounts of methanol to the gas-phase at and around the location of the CO thermal desorption front in a protoplanetary disk. The impact of thermal co-desorption of CH3OH with CO as a grain-gas bridge mechanism is compared with that of UV induced photodesorption and chemisorption.

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