scholarly journals Revisiting the reactivity between HCO and CH3 on interstellar grain surfaces

2020 ◽  
Vol 493 (2) ◽  
pp. 2523-2527 ◽  
Author(s):  
J Enrique-Romero ◽  
S Álvarez-Barcia ◽  
F J Kolb ◽  
A Rimola ◽  
C Ceccarelli ◽  
...  
Keyword(s):  
Water Molecule ◽  
Energy Barrier ◽  
Density Functional ◽  
High Energy ◽  
Functional Theory ◽  
Radical Coupling ◽  
High Energy Barrier ◽  
Single Water Molecule ◽  
Complex Organic

ABSTRACT The formation of interstellar complex organic molecules is currently thought to be dominated by the barrierless coupling between radicals on the interstellar icy grain surfaces. Previous standard density functional theory (DFT) results on the reactivity between CH3 and HCO on amorphous water surfaces showed that the formation of CH4 + CO by H transfer from HCO to CH3 assisted by water molecules of the ice was the dominant channel. However, the adopted description of the electronic structure of the biradical (i.e. CH3/HCO) system was inadequate [without the broken-symmetry (BS) approach]. In this work, we revisit the original results by means of BS-DFT both in gas phase and with one water molecule simulating the role of the ice. Results indicate that the adoption of BS-DFT is mandatory to describe properly biradical systems. In the presence of the single water molecule, the water-assisted H transfer exhibits a high energy barrier. In contrast, CH3CHO formation is found to be barrierless. However, direct H transfer from HCO to CH3 to give CO and CH4 presents a very low energy barrier, hence being a potential competitive channel to the radical coupling and indicating, moreover, that the physical insights of the original work remain valid.

First principle simulation on oxidation mechanism of diethyl ether by nitrogen dioxide

2015 ◽  
Vol 14 (03) ◽  
pp. 1550020 ◽  
Author(s):  
Yuan Yuan ◽  
Wei Hu ◽  
Xuhui Chi ◽  
Cuihua Li ◽  
Dayong Gui ◽  
...  
Keyword(s):  
Diethyl Ether ◽  
Energy Barrier ◽  
Density Functional ◽  
Oxidation Process ◽  
Oxidation Mechanism ◽  
High Energy ◽  
First Principle ◽  
Functional Theory ◽  
The Third ◽  
High Energy Barrier

The oxidation mechanism of diethyl ethers by NO2was carried out using density functional theory (DFT) at the B3LYP/6-31+G (d, p) level. The oxidation process of ether follows four steps. First, the diethyl ether reacts with NO2to produce HNO2and diethyl ether radical with an energy barrier of 20.62 kcal ⋅ mol-1. Then, the diethyl ether radical formed in the first step directly combines with NO2to form CH3CH ( ONO ) OCH2CH3. In the third step, the CH3CH ( ONO ) OCH2CH3was further decomposed into the CH3CH2ONO and CH3CHO with a moderately high energy barrier of 32.87 kcal ⋅ mol-1. Finally, the CH3CH2ONO continues to react with NO2to yield CH3CHO , HNO2and NO with an energy barrier of 28.13 kcal ⋅ mol-1. The calculated oxidation mechanism agrees well with Nishiguchi and Okamoto's experiment and proposal.

A THEORETICAL STUDY OF UNSATURATED OLEFIN HYDROGENATION AND ISOMERIZATION ON Pd(111)

2008 ◽  
Vol 15 (03) ◽  
pp. 249-259 ◽  
Author(s):  
PATRICIA G. BELELLI ◽  
NORBERTO J. CASTELLANI
Keyword(s):  
Energy Barrier ◽  
Density Functional ◽  
Theoretical Study ◽  
High Energy ◽  
Slab Model ◽  
Functional Theory ◽  
Hydrogen Addition ◽  
High Energy Barrier ◽  
The Density Functional Theory ◽  
Cis And Trans

The addition of hydrogen to the carbon–carbon double bond of 2-butenes adsorbed on Pd (111) was studied within the density functional theory (DFT) and using a periodic slab model. For that purpose, the Horiuti–Polanyi mechanisms for both complete hydrogenation and isomerization were considered. The hydrogenation of cis and trans-2-butene to produce butane proceeds via the formation of eclipsed and staggered-2-butyl intermediates, respectively. In both cases, a relatively high energy barrier to produce the half-hydrogenated intermediate makes the first hydrogen addition the slowest step of the reaction. The competitive production of trans-2-butene from cis-2-butene requires the conversion from the eclipsed-2-butyl to the staggered-2-butyl isomer. As the corresponding energy barrier is relatively small and because the first of these isomers is less stable than the second, an easy conversion is predicted.

DFT study on the hydrolysis of metsulfuron-methyl: A sulfonylurea herbicide

2018 ◽  
Vol 17 (08) ◽  
pp. 1850050 ◽  
Author(s):  
Qiuhan Luo ◽  
Gang Li ◽  
Junping Xiao ◽  
Chunhui Yin ◽  
Yahui He ◽  
...  
Keyword(s):  
Free Energy ◽  
Water Molecule ◽  
Carbonyl Group ◽  
Energy Barrier ◽  
Density Functional ◽  
Free Energy Barrier ◽  
Functional Theory ◽  
Metsulfuron Methyl ◽  
Catalytic Role ◽  
Hydrolysis Of

Sulfonylureas are an important group of herbicides widely used for a range of weeds and grasses control particularly in cereals. However, some of them tend to persist for years in environments. Hydrolysis is the primary pathway for their degradation. To understand the hydrolysis behavior of sulfonylurea herbicides, the hydrolysis mechanism of metsulfuron-methyl, a typical sulfonylurea, was investigated using density functional theory (DFT) at the B3LYP/6-31[Formula: see text]G(d,p) level. The hydrolysis of metsulfuron-methyl resembles nucleophilic substitution by a water molecule attacking the carbonyl group from aryl side (pathway a) or from heterocycle side (pathway b). In the direct hydrolysis, the carbonyl group is directly attacked by one water molecule to form benzene sulfonamide or heterocyclic amine; the free energy barrier is about 52–58[Formula: see text]kcal[Formula: see text]mol[Formula: see text]. In the autocatalytic hydrolysis, with the second water molecule acting as a catalyst, the free energy barrier, which is about 43–45[Formula: see text]kcal[Formula: see text]mol[Formula: see text], is remarkably reduced by about 11[Formula: see text]kcal[Formula: see text]mol[Formula: see text]. It is obvious that water molecules play a significant catalytic role during the hydrolysis of sulfonylureas.

Theoretical Insights into the Role of Water Molecule in The Aqueous/Cu(111) Interface during Corrosion Pathway

2014 ◽  
Vol 19 (4) ◽  
pp. 235-240
Author(s):  
Jun Hu ◽  
Xiao-yong Fan ◽  
Chao-Ming Wang
Keyword(s):  
Water Molecule ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Adsorbed Water ◽  
Dipole Interaction ◽  
Hydrogen Atoms ◽  
Functional Theory ◽  
Adsorbed Water Molecule ◽  
The One

The absorption and possible reaction paths during corrosion have been systematically identified at the molecular level by us-ing density functional theory calculations. The results show that the co-adsorbed water molecule has a two-fold impact on the corrosive kinetics process. The one is the solvation effect, where water molecule affects the various reactions through ion dipole interaction, without bond fracture and formation. Another is the H-transfer mediator, where the bond of co-adsorbed water molecule breaks and regenerates in order to transfer hydrogen atoms.

scholarly journals Role of Mg Impurity in the Water Adsorption over Low-Index Surfaces of Calcium Silicates: A DFT-D Study

Minerals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 665
Author(s):  
Chongchong Qi ◽  
Qiusong Chen ◽  
Andy Fourie
Keyword(s):  
Water Molecule ◽  
Density Functional ◽  
Water Adsorption ◽  
Dissociative Adsorption ◽  
Mg Doping ◽  
Calcium Silicates ◽  
Single Water Molecule ◽  
The Impact ◽  
Mg Doped

Calcium silicates are the most predominant phases in ordinary Portland cement, inside which magnesium is one of the momentous impurities. In this work, using the first-principles density functional theory (DFT), the impurity formation energy (Efor) of Mg substituting Ca was calculated. The adsorption energy (Ead) and configuration of the single water molecule over Mg-doped β-dicalcium silicate (β-C2S) and M3-tricalcium silicate (M3-C3S) surfaces were investigated. The obtained Mg-doped results were compared with the pristine results to reveal the impact of Mg doping. The results show that the Efor was positive for all but one of the calcium silicates surfaces (ranged from −0.02 eV to 1.58 eV), indicating the Mg substituting for Ca was not energetically favorable. The Ead of a water molecule on Mg-doped β-C2S surfaces ranged from –0.598 eV to −1.249 eV with the molecular adsorption being the energetically favorable form. In contrast, the Ead on M3-C3S surfaces ranged from −0.699 eV to −4.008 eV and the more energetically favorable adsorption on M3-C3S surfaces was dissociative adsorption. The influence of Mg doping was important since it affected the reactivity of surface Ca/Mg sites, the Ead of the single water adsorption, as well as the adsorption configuration compared with the water adsorption on pristine surfaces.

Influence of water on the CH3O˙ + O2 → CH2O + HO2˙ reaction

2019 ◽  
Vol 21 (28) ◽  
pp. 15734-15741 ◽  
Author(s):  
Subhasish Mallick ◽  
Amit Kumar ◽  
Brijesh Kumar Mishra ◽  
Pradeep Kumar
Keyword(s):  
Density Functional Theory ◽  
Electronic Structure ◽  
Water Molecule ◽  
Density Functional ◽  
Electronic Structure Calculations ◽  
Functional Theory ◽  
Influence Of Water ◽  
Single Water Molecule ◽  
Structure Calculations

Electronic structure calculations employing density functional theory have been used to study the effect of a single water molecule on the CH3O˙ + O2 → CH2O + HO2˙ reaction.

On the Ag+–cytosine interaction: the effect of microhydration probed by IR optical spectroscopy and density functional theory

2015 ◽  
Vol 17 (39) ◽  
pp. 25915-25924 ◽  
Author(s):  
Matias Berdakin ◽  
Vincent Steinmetz ◽  
Philippe Maitre ◽  
Gustavo A. Pino
Keyword(s):  
Density Functional Theory ◽  
Water Molecule ◽  
Optical Spectroscopy ◽  
Density Functional ◽  
Functional Theory ◽  
Single Water Molecule

Single water molecule hydration stabilizes two quasi-isoenergetic complexes of cytosine⋯Ag+.

Theoretical Study on Aggregation of Nuclei-Containing Gas Phase

2017 ◽  
Author(s):  
Zhong Lan ◽  
Quan Xue ◽  
Xuehu Ma ◽  
Di Wang ◽  
Kejian Cao ◽  
...  
Keyword(s):  
Water Molecule ◽  
Gas Phase ◽  
Energy Barrier ◽  
Density Functional ◽  
Water Clusters ◽  
Condensation Nucleus ◽  
Condensation Process ◽  
Functional Theory ◽  
Particle Properties ◽  
Molecule Aggregation

Haze is a kind of typical heterogeneous nucleation phenomenon in gas phase condensation process. The existence of dust nucleus may induce water molecule aggregation among vapor phase under a certain humidity. In this article, we try to use Density Functional Theory simulation to explore the evolution mechanism of water molecule aggregation influenced by condensation nucleus from the perspective of molecules assembling. We can get the following results: the subcooling degree and physicochemical properties of nucleation center affect the hydrogen bond within the water clusters and the transformation energy barrier of water molecule aggregation tendency. Water vapor begins to heterogeneously condense or forms aggregation humidity in a certain condition based on the center of condensation nuclei. The analysis shows that the effect law of the degree and scale of aggregation or phase transition are influenced by the change of gas phase partial pressure, supersaturated degree along with particle properties. As the energy barrier of nucleation free energy decreases, the formation of water clusters will be easier.

scholarly journals High Throughput Virtual Screening of 230 Billion Molecular Solar Heat Battery Candidates

2020 ◽  
Author(s):  
Mads Koerstz ◽  
Anders S. Christensen ◽  
Kurt V. Mikkelsen ◽  
Mogens Brøndsted Nielsen ◽  
Jan H. Jensen
Keyword(s):  
Free Energy ◽  
Energy Barrier ◽  
Density Functional ◽  
Parent Compound ◽  
High Energy ◽  
Back Reaction ◽  
Free Energy Barrier ◽  
Functional Theory ◽  
Practical Applications ◽  
Quantum Chemical Methods

<div>The dihydroazulene/vinylheptafulvene (DHA/VHF) thermocouple is a promising can- didate for thermal heat batteries that absorb and store solar energy as chemical energy without the need for insulation. However, in order to be viable the energy storage capacity and lifetime of the high energy form (i.e. the free energy barrier to the back reaction) of the canonical parent compound must be increased significantly to be of practical use. We use semiempirical quantum chemical methods, machine learning, and density functional theory to virtually screen over 230 billion substituted DHA molecules to identify promis- ing candidates. We identify a molecule with a predicted energy density of 0.38 kJ/g, which is significantly larger than the 0.14 kJ/g computed for the parent compound. The free energy barrier to the back reaction is 11 kJ/mol higher than the parent compound, which should correspond to a half-life of about 10 days - 4 months. This is considerably longer than the 3-39 hours (depending on solvent) observed for the parent compound and sufficiently long for many practical applications. However, the main conclusion of this study is that there are no molecules among the 230 billion with a storage density approaching 1 kJ/g.<br></div>

scholarly journals High Throughput Virtual Screening of 230 Billion Molecular Solar Heat Battery Candidates

2020 ◽  
Author(s):  
Mads Koerstz ◽  
Anders S. Christensen ◽  
Kurt V. Mikkelsen ◽  
Mogens Brøndsted Nielsen ◽  
Jan H. Jensen
Keyword(s):  
Free Energy ◽  
Energy Barrier ◽  
Density Functional ◽  
Parent Compound ◽  
High Energy ◽  
Back Reaction ◽  
Free Energy Barrier ◽  
Functional Theory ◽  
Practical Applications ◽  
Quantum Chemical Methods

<div>The dihydroazulene/vinylheptafulvene (DHA/VHF) thermocouple is a promising can- didate for thermal heat batteries that absorb and store solar energy as chemical energy without the need for insulation. However, in order to be viable the energy storage capacity and lifetime of the high energy form (i.e. the free energy barrier to the back reaction) of the canonical parent compound must be increased significantly to be of practical use. We use semiempirical quantum chemical methods, machine learning, and density functional theory to virtually screen over 230 billion substituted DHA molecules to identify promis- ing candidates. We identify a molecule with a predicted energy density of 0.38 kJ/g, which is significantly larger than the 0.14 kJ/g computed for the parent compound. The free energy barrier to the back reaction is 11 kJ/mol higher than the parent compound, which should correspond to a half-life of about 10 days - 4 months. This is considerably longer than the 3-39 hours (depending on solvent) observed for the parent compound and sufficiently long for many practical applications. However, the main conclusion of this study is that there are no molecules among the 230 billion with a storage density approaching 1 kJ/g.<br></div>

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