scholarly journals Thermal desorption of formamide and methylamine from graphite and amorphous water ice surfaces

2019 ◽  
Vol 15 (S350) ◽  
pp. 370-371
Author(s):  
Henda Chaabouni ◽  
Stephan Diana ◽  
Thanh Nguyen
Keyword(s):  
Energy Distribution ◽  
Thermal Desorption ◽  
Interstellar Dust ◽  
Binding Energies ◽  
Desorption Energy ◽  
Exponential Factor ◽  
Water Ice ◽  
Ice Surface ◽  
Crystalline Water ◽  
Best Fit

AbstractThermal desorption experiments of Formamide (NH2CHO) and methylamine (CH3NH2) were performed in LERMA-Cergy laboratory to determine the values of the desorption energies of formamide and methylamine from analogues of interstellar dust grain surfaces, and to understand their interaction with water ice. We found that more than 95 % of solid NH2CHO diffuses through the np-ASW ice surface towards the graphitic substrate, and is released into the gas phase with a desorption energy distribution Edes = (7460 – 9380) K, measured with the best-fit pre-exponential factor A=1018 s-1. Whereas, the desorption energy distribution of methylamine from the np-ASW ice surface (Edes =3850-8420 K) is measured with the best-fit pre-exponential factor A=1012s-1. A fraction of solid methylamine, of about 0.15 monolayer diffuses through the water ice surface towards the HOPG substrate, and desorbs later, with higher binding energies (5050-8420 K), which exceed that of the crystalline water ice (Edes =4930 K), calculated with the same pre-exponential factor A=1012 s-1.

scholarly journals Thermal desorption of formamide and methylamine from graphite and amorphous water ice surfaces

2018 ◽  
Vol 612 ◽  
pp. A47 ◽  
Author(s):  
H. Chaabouni ◽  
S. Diana ◽  
T. Nguyen ◽  
F. Dulieu
Keyword(s):  
Energy Distribution ◽  
Gas Phase ◽  
Thermal Desorption ◽  
Binding Energies ◽  
Desorption Energy ◽  
Exponential Factor ◽  
Water Ice ◽  
Ice Surface ◽  
Ice Surfaces ◽  
Best Fit

Context. Formamide (NH2CHO) and methylamine (CH3NH2) are known to be the most abundant amine-containing molecules in many astrophysical environments. The presence of these molecules in the gas phase may result from thermal desorption of interstellar ices. Aims. The aim of this work is to determine the values of the desorption energies of formamide and methylamine from analogues of interstellar dust grain surfaces and to understand their interaction with water ice. Methods. Temperature programmed desorption (TPD) experiments of formamide and methylamine ices were performed in the sub-monolayer and monolayer regimes on graphite (HOPG) and non-porous amorphous solid water (np-ASW) ice surfaces at temperatures 40–240 K. The desorption energy distributions of these two molecules were calculated from TPD measurements using a set of independent Polanyi–Wigner equations. Results. The maximum of the desorption of formamide from both graphite and ASW ice surfaces occurs at 176 K after the desorption of H2O molecules, whereas the desorption profile of methylamine depends strongly on the substrate. Solid methylamine starts to desorb below 100 K from the graphite surface. Its desorption from the water ice surface occurs after 120 K and stops during the water ice sublimation around 150 K. It continues to desorb from the graphite surface at temperatures higher than160 K. Conclusions. More than 95% of solid NH2CHO diffuses through the np-ASW ice surface towards the graphitic substrate and is released into the gas phase with a desorption energy distribution Edes = 7460–9380 K, which is measured with the best-fit pre-exponential factor A = 1018 s−1. However, the desorption energy distribution of methylamine from the np-ASW ice surface (Edes = 3850–8420 K) is measured with the best-fit pre-exponential factor A = 1012 s−1. A fraction of solid methylamine monolayer of roughly 0.15 diffuses through the water ice surface towards the HOPG substrate. This small amount of methylamine desorbs later with higher binding energies (5050–8420 K) that exceed that of the crystalline water ice (Edes = 4930 K), which is calculated with the same pre-exponential factor A = 1012 s−1. The best wetting ability of methylamine compared to H2O molecules makes CH3NH2 molecules a refractory species for low coverage. Other binding energies of astrophysical relevant molecules are gathered and compared, but we could not link the chemical functional groups (amino, methyl, hydroxyl, and carbonyl) with the binding energy properties. Implications of these high binding energies are discussed.

The vibrational signatures of polyaromatic hydrocarbons on an ice surface

2019 ◽  
Vol 15 (S350) ◽  
pp. 468-470
Author(s):  
Victoria H.J. Clark ◽  
David M. Benoit
Keyword(s):  
Vibrational Spectra ◽  
Density Functional ◽  
Polyaromatic Hydrocarbons ◽  
Functional Theory ◽  
Water Ice ◽  
Aromatic Molecules ◽  
Ice Surface ◽  
Vibrational Anharmonicity ◽  
Potential Energy Landscape ◽  
Crystalline Water

AbstractWe use quantum chemical techniques to model the vibrational spectra of small aromatic molecules on a proton-ordered hexagonal crystalline water ice (XIh) model. We achieve a good agreement with experimental data by accounting for vibrational anharmonicity and correcting the potential energy landscape for known failures of density functional theory. A standard harmonic description of the vibrational spectra only leads to a broad qualitative agreement.

scholarly journals Molecular Orbital Calculations of Water-Ice Surface Interactions

1978 ◽  
Vol 21 (85) ◽  
pp. 565-580
Author(s):  
Patricia L. M. Plummer
Keyword(s):  
Ion Pairs ◽  
Binding Energies ◽  
Detailed Knowledge ◽  
Molecular Orbital Calculations ◽  
Physical Situation ◽  
Surface Binding ◽  
Water Ice ◽  
Ice Surface ◽  
Semi Empirical ◽  
Free Monomer

AbstractDetailed knowledge of the energetics of the interaction of a water monomer with an ice surface is important in understanding the factors which control both the nucleation and the growth of ice. In this work we model this interaction by using a small section of an ice surface and semi-empirical quantum-mechanical calculations of the CNDO/INDO type to investigate the energetics of a gas-phase molecule approaching the surface. In the attempt to simplify the system as much as possible while retaining the essential features of the "real" physical situation, 13 water molecules arranged in the lattice positions for ice Ih were used to represent the surface. Electron-density plots for both basal and prism surfaces were generated. Potential-energy curves were calculated for a monomer approaching a number of different sites on each type of surface. Monomer-surface binding energies varied from approximately 17 to 33 kJ/mol for the surface sites examined. Ion pairs of the H30+-OH- type were included in the surface and their effect on the energy of interaction with an incoming monomer calculated. For these studies no distortion of the ice surface was allowed. The energies found follow the same trends as observed for a free monomer-ion interaction.

scholarly journals Computing Binding Energies of Interstellar Molecules by Semiempirical Quantum Methods: Comparison Between DFT and GFN2 on Crystalline Ice

2021 ◽  
pp. 632-645
Author(s):  
Aurèle Germain ◽  
Marta Corno ◽  
Piero Ugliengo
Keyword(s):  
Gas Phase ◽  
Water Clusters ◽  
Binding Energies ◽  
Water Ice ◽  
Small Water ◽  
Adsorption Processes ◽  
Quantum Approach ◽  
Crystalline Water ◽  
Ordered Water ◽  
Grain Surface

AbstractInterstellar Grains (IGs) spread in the Interstellar Medium (ISM) host a multitude of chemical reactions that could lead to the production of interstellar Complex Organic Molecules (iCOMs), relevant in the context of prebiotic chemistry. These IGs are composed of a silicate-based core covered by several layers of amorphous water ice, known as a grain mantle. Molecules from the ISM gas-phase can be adsorbed at the grain surfaces, diffuse and react to give iCOMs and ultimately desorbed back to the gas phase. Thus, the study of the Binding Energy (BE) of these molecules at the water ice grain surface is important to understand the molecular composition of the ISM and its evolution in time. In this paper, we propose to use a recently developed semiempirical quantum approach, named GFN-xTB, and more precisely the GFN2 method, to compute the BE of several molecular species at the crystalline water ice slab model. This method is very cheap in term of computing power and time and was already showed in a previous work to be very accurate with small water clusters. To support our proposition, we decided to use, as a benchmark, the recent work published by some of us in which a crystalline model of proton-ordered water ice (P-ice) was adopted to predict the BEs of 21 molecules relevant in the ISM. The relatively good results obtained confirm GFN2 as the method of choice to model adsorption processes occurring at the icy grains in the ISM. The only notable exception was for the CO molecule, in which both structure and BE are badly predicted by GFN2, a real pity due to the relevance of CO in astrochemistry.

scholarly journals Using Surface Science Techniques to Investigate the Interaction of Acetonitrile with Dust Grain Analogue Surfaces

2021 ◽  
Author(s):  
Emily R. Ingman ◽  
Amber Shepherd ◽  
Wendy A. Brown
Keyword(s):  
Surface Science ◽  
Thermal Processing ◽  
Desorption Energy ◽  
Water Ice ◽  
Ice Surface ◽  
Coverage Analysis ◽  
Wide Range ◽  
Reflection Absorption Infrared Spectroscopy ◽  
Temperature Programmed ◽  
Dust Grain

Surface science methodologies, such as reflection-absorption infrared spectroscopy (RAIRS) and temperature programmed desorption (TPD), are ideally suited to studying the interaction of molecules with model astrophysical surfaces. Here we describe the use of RAIRS and TPD to investigate the adsorption, interactions and thermal processing of acetonitrile and water containing model ices grown under astrophysical conditions on a graphitic dust grain analogue surface. Experiments show that acetonitrile physisorbs on the graphitic surface at all exposures. At the lowest coverages, repulsions between the molecules lead to a decreasing desorption energy with increasing coverage. Analysis of TPD data gives monolayer desorption energies ranging from 28.8 - 39.2 kJ mol-1 and an average multilayer desorption energy of 43.8 kJ mol-1. When acetonitrile is adsorbed in the presence of water ice, the desorption energy of monolayer acetonitrile shows evidence of desorption with a wide range of energies. An estimate of the desorption energy of acetonitrile from CI shows that it is increased to ~37 kJ mol-1 at the lowest exposures of acetonitrile. Amorphous water ice also traps acetonitrile on the graphite surface past its natural desorption temperature, leading to volcano and co-desorption. RAIRS data show that the C≡N vibration shifts, indicative of an interaction between the acetonitrile and the water ice surface.

scholarly journals Molecular Orbital Calculations of Water-Ice Surface Interactions

1978 ◽  
Vol 21 (85) ◽  
pp. 565-580 ◽  
Author(s):  
Patricia L. M. Plummer
Keyword(s):  
Ion Pairs ◽  
Binding Energies ◽  
Detailed Knowledge ◽  
Molecular Orbital Calculations ◽  
Physical Situation ◽  
Surface Binding ◽  
Water Ice ◽  
Ice Surface ◽  
Semi Empirical ◽  
Free Monomer

Abstract Detailed knowledge of the energetics of the interaction of a water monomer with an ice surface is important in understanding the factors which control both the nucleation and the growth of ice. In this work we model this interaction by using a small section of an ice surface and semi-empirical quantum-mechanical calculations of the CNDO/INDO type to investigate the energetics of a gas-phase molecule approaching the surface. In the attempt to simplify the system as much as possible while retaining the essential features of the "real" physical situation, 13 water molecules arranged in the lattice positions for ice Ih were used to represent the surface. Electron-density plots for both basal and prism surfaces were generated. Potential-energy curves were calculated for a monomer approaching a number of different sites on each type of surface. Monomer-surface binding energies varied from approximately 17 to 33 kJ/mol for the surface sites examined. Ion pairs of the H30 +-OH- type were included in the surface and their effect on the energy of interaction with an incoming monomer calculated. For these studies no distortion of the ice surface was allowed. The energies found follow the same trends as observed for a free monomer-ion interaction.

scholarly journals Connecting complex networks to nonadditive entropies

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
R. M. de Oliveira ◽  
Samuraí Brito ◽  
L. R. da Silva ◽  
Constantino Tsallis
Keyword(s):  
Statistical Mechanics ◽  
Energy Distribution ◽  
Complex Networks ◽  
Wide Class ◽  
Scale Invariant ◽  
Nonlocal Effects ◽  
Geometric Problem ◽  
Exponential Factor ◽  
Research Areas ◽  
Quasi Stationary State

AbstractBoltzmann–Gibbs statistical mechanics applies satisfactorily to a plethora of systems. It fails however for complex systems generically involving nonlocal space–time entanglement. Its generalization based on nonadditive q-entropies adequately handles a wide class of such systems. We show here that scale-invariant networks belong to this class. We numerically study a d-dimensional geographically located network with weighted links and exhibit its ‘energy’ distribution per site at its quasi-stationary state. Our results strongly suggest a correspondence between the random geometric problem and a class of thermal problems within the generalised thermostatistics. The Boltzmann–Gibbs exponential factor is generically substituted by its q-generalisation, and is recovered in the $$q=1$$ q = 1 limit when the nonlocal effects fade away. The present connection should cross-fertilise experiments in both research areas.

Influence of submonolayer sodium adsorption on the photoemission of the Cu(111)/water ice surface

2006 ◽  
Vol 125 (22) ◽  
pp. 224702 ◽  
Author(s):  
Tomas Vondrak ◽  
John M. C. Plane ◽  
Stephen R. Meech
Keyword(s):  
Water Ice ◽  
Ice Surface

Structural and Phase Transitions on Water Ice Surface Under HCl Exposure: Implication for Stratosphere Conditions

1998 ◽  
Vol 05 (01) ◽  
pp. 437-441
Author(s):  
N. M. Persiantseva ◽  
O. B. Popovicheva ◽  
T. V. Rakhimova
Keyword(s):  
Phase Transitions ◽  
Pressure Range ◽  
Phase State ◽  
Amorphous Solid ◽  
Surface Concentration ◽  
Uptake Kinetics ◽  
Water Ice ◽  
Uptake Efficiency ◽  
Ice Surface ◽  
Characteristic Values

The HCl-ice interaction has been investigated over a wide HCl pressure range of 10-7–10-4 Torr and ice temperatures 150–240 K. The Three characteristic values for HCl uptake efficiency were obtained which indicate the change of phase state and structure of the ice surface at increasing HCl pressure. The low value γ ≈ 0.1 ± 0.02 corresponds to HCl vapor interaction with pure ice and is realized at the atmosphere conditions. The value γ ≈ 0.5 ± 0.1 indicates the formation of hexahydrate HCl • 6H 2 O with increase of HCl pressure. And the largest value of γ ≈ 0.8 ± 0.1 is observed at appearance of liquid or amorphous solid 4:1 H 2O:HCl. The HCl uptake kinetics is analyzed. The flow of HCl molecules from the ice surface into the bulk is shown to play an important role in the redistribution of HCl molecules. It defines a low surface concentration of the adsorbed HCl molecules under stratospher condition at early times of interaction.

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