scholarly journals Compilation and evaluation of gas phase diffusion coefficients of halogenated organic compounds

2018 ◽  
Vol 5 (7) ◽  
pp. 171936 ◽  
Author(s):  
Wenjun Gu ◽  
Peng Cheng ◽  
Mingjin Tang
Keyword(s):  
Gas Phase ◽  
Diffusion Coefficients ◽  
Input Parameter ◽  
Empirical Method ◽  
Trace Gas ◽  
Temperature And Pressure ◽  
Organic Halogens ◽  
Semi Empirical ◽  
Method Show ◽  
Good Agreement

Organic halogens are of great environmental and climatic concern. In this work, we have compiled their gas phase diffusivities (pressure-normalized diffusion coefficients) in a variety of bath gases experimentally measured by previous studies. It is found that diffusivities estimated using Fuller's semi-empirical method agree very well with measured values for organic halogens. In addition, we find that at a given temperature and pressure, different molecules exhibit very similar mean free paths in the same bath gas, and then propose a method to estimate mean free paths in different bath gases. For example, the pressure-normalized mean free paths are estimated to be 90, 350, 90, 80, 120 nm atm in air (and N 2 /O 2 ), He, argon, CO 2 and CH 4 , respectively, with estimated errors of around ±25%. A generic method, which requires less input parameter than Fuller's method, is proposed to calculate gas phase diffusivities. We find that gas phase diffusivities in He (and air as well) calculated using our method show fairly good agreement with those measured experimentally and estimated using Fuller's method. Our method is particularly useful for the estimation of gas phase diffusivities when the trace gas contains atoms whose diffusion volumes are not known.

scholarly journals Compilation and evaluation of gas-phase diffusion coefficients of inorganic reactive trace gases in the atmosphere

2014 ◽  
Vol 14 (10) ◽  
pp. 15645-15682 ◽  
Author(s):  
M. J. Tang ◽  
R. A. Cox ◽  
M. Kalberer
Keyword(s):  
Gas Phase ◽  
Atmospheric Chemistry ◽  
Diffusion Coefficients ◽  
Trace Gases ◽  
Empirical Method ◽  
Phase Diffusion ◽  
Reactive Trace Gases ◽  
Pressure Independent ◽  
Semi Empirical ◽  
First Time

Abstract. Diffusion of gas molecules to the surface is the first step for all gas-surface reactions. Gas phase diffusion can influence and sometimes even limit the overall rates of these reactions; however, there is no database of the gas phase diffusion coefficients of atmospheric reactive trace gases. Here we compile and evaluate, for the first time, the diffusivities (pressure-independent diffusion coefficients) of atmospheric inorganic reactive trace gases reported in the literature. The measured diffusivities are then compared with estimated values using a semi-empirical method developed by Fuller et al. (1966). The diffusivities estimated using Fuller's method are typically found to be in good agreement with the measured values within ±30%, and therefore Fuller's method can be used to estimate the diffusivities of trace gases for which experimental data are not available. The two experimental methods used in the atmospheric chemistry community to measure the gas phase diffusion coefficients are also discussed.

scholarly journals Compilation and evaluation of gas phase diffusion coefficients of reactive trace gases in the atmosphere: volume 1. Inorganic compounds

2014 ◽  
Vol 14 (17) ◽  
pp. 9233-9247 ◽  
Author(s):  
M. J. Tang ◽  
R. A. Cox ◽  
M. Kalberer
Keyword(s):  
Gas Phase ◽  
Atmospheric Chemistry ◽  
Diffusion Coefficients ◽  
Inorganic Compounds ◽  
Trace Gases ◽  
Empirical Method ◽  
Phase Diffusion ◽  
Reactive Trace Gases ◽  
Pressure Independent ◽  
Semi Empirical

Abstract. Diffusion of gas molecules to the surface is the first step for all gas–surface reactions. Gas phase diffusion can influence and sometimes even limit the overall rates of these reactions; however, there is no database of the gas phase diffusion coefficients of atmospheric reactive trace gases. Here we compile and evaluate, for the first time, the diffusivities (pressure-independent diffusion coefficients) of atmospheric inorganic reactive trace gases reported in the literature. The measured diffusivities are then compared with estimated values using a semi-empirical method developed by Fuller et al. (1966). The diffusivities estimated using Fuller's method are typically found to be in good agreement with the measured values within ±30%, and therefore Fuller's method can be used to estimate the diffusivities of trace gases for which experimental data are not available. The two experimental methods used in the atmospheric chemistry community to measure the gas phase diffusion coefficients are also discussed. A different version of this compilation/evaluation, which will be updated when new data become available, is uploaded online (https://sites.google.com/site/mingjintang/home/diffusion).

Polyalanine gas phase acidities determination and conformational space analysis by genetic algorithm assessment

2019 ◽  
Author(s):  
Chem Int
Keyword(s):  
Genetic Algorithm ◽  
Gas Phase ◽  
Energy Surface ◽  
Conformational Space ◽  
Am1 Method ◽  
The One ◽  
Semi Empirical ◽  
Global And Local ◽  
Formation Energies ◽  
Good Agreement

The genetic algorithm, based on the Multi-Niche Crowding (MNC) method, coupled with the semi-empirical AM1 method is used to analyze the potential energy surface of some polypeptides containing cysteine. Calculating the formation energies of these systems in both neutral and deprotonated states, we deducted their enthalpy of deprotonation (ΔHacid) and we identified the types of rearrangement of these systems when isolated. Deprotonation occurs at the level of the alone acid site characterizing these peptides namely the thiol. The values obtained for the deprotonation enthalpies of polypeptides AlaCysNH2, Ala2CysNH2, Ala3CysNH2, Ala4CysNH2, CysAlaNH2 and CysAla2NH2 are in the order of 331.3 kcal/mol, 322.9 kcal/mol, 313.8 kcal/mol, 312.9 kcal/mol, 325.1 kcal/mol and 317.3 kcal/mol, respectively. The location of global and local minima of these polypeptides shows that they are rearranged in two forms of secondary structures namely helical and globular forms. The obtained results are in good agreement with the experimental ones, on the one hand, and with those from other methods in the theoretical calculation, on the other hand. Therefore, the N-cysteine is more acidic than their homologous C-Cysteine and for this series of plolyalanines, the acidity in the gas phase increased with the peptide chain length.

scholarly journals Super-Heavy Elements (Z = 100-109) Treated as Calcium Clusters: First Ionization Energies

2020 ◽  
Author(s):  
Robson de Farias
Keyword(s):  
Quantum Mechanics ◽  
Relativistic Quantum ◽  
Empirical Method ◽  
Heavy Elements ◽  
Relativistic Quantum Mechanics ◽  
Ionization Energies ◽  
Semi Empirical ◽  
Good Agreement

<p>In the present work, it is shown that the first ionization energies for super-heavy elements (Z= 100-109) can be calculated by a semi-empirical method, if the super-heavy elements are treated (modelled) as calcium clusters. The values calculated in the present work are in good agreement compared with those from literature (modelling the super-heavy elements themselves, based on relativistic quantum mechanics). </p>

Au–Ir nanoalloy nucleation during the gas-phase condensation: a comprehensive MD study including different effects

2018 ◽  
Vol 5 (6) ◽  
pp. 1445-1457 ◽  
Author(s):  
Mohsen Abbaspour ◽  
Hamed Akbarzadeh ◽  
Zahra Valizadeh
Keyword(s):  
Gas Phase ◽  
Experimental Results ◽  
Temperature And Pressure ◽  
Increasing Temperature ◽  
Good Agreement

The number of formed clusters and their size increases with the increasing temperature and pressure, which is in good agreement with the experimental results.

Crystal Structure Optimization and Semi-Empirical Quantum Chemical Calculations of N-(3,4-Dichlorophenyl)-3-Oxo-Butanamide

2012 ◽  
Vol 620 ◽  
pp. 82-86
Author(s):  
Mukesh M. Jotani
Keyword(s):  
Crystal Structure ◽  
Molecular Electrostatic Potential ◽  
Crystal Packing ◽  
Empirical Method ◽  
Molecular Orbital Calculations ◽  
X Ray ◽  
Semi Empirical ◽  
Packing Interactions ◽  
Optimized Geometries ◽  
Good Agreement

The crystal structure of N-(3,4-Dichlorophenyl)-3-oxobutanamide (I) is optimized by semi-empirical methods using MOPAC2009 program. The optimized geometries from both Austin Model 1 (AM1) and Parametrization Model 6 (PM6) describe the conformational discrepancy and crystal packing. The energy minimized structures from both the models are in good agreement with X-ray crystal data. The intramolecular charge transfer interactions are studied from the molecular orbital calculations. The parametric molecular electrostatic potential (PMEP) calculated by AM1 semi-empirical method shows the involvement of oxygen and chlorine atoms in the crystal packing interactions. The aromaticity of phenyl ring in the structure is determined using HOMED calculations.

New Semi-Empirical Method for Alloys

1992 ◽  
Vol 278 ◽  
Author(s):  
Guillermo Bozzolo ◽  
John Ferrante
Keyword(s):  
Defect Formation ◽  
Empirical Method ◽  
Experimental Results ◽  
New Method ◽  
Surface Energies ◽  
Computational Simplicity ◽  
Alloy Properties ◽  
Semi Empirical ◽  
Formation Energies ◽  
Good Agreement

AbstractWe introduce a new semi-empirical method for calculating alloy properties. The method Is based on the concepts of equivalent crystal theory of defect formation energies in elemental solids. With this new method we predict heats of formation, lattice parameters, surface energies, segregation senergies and other properties of several binary alloys of fcc (Cu, NI, Ag, Au, Al, Fe, Pd and Pt) and bcc (Cr, Mo, Fe, V) elements. The method is characterized for its extreme computational simplicity and good agreement with experimental results. Several applications of the method are discussed.

scholarly journals Super-Heavy Elements (Z = 100-109) Treated as Calcium Clusters: First Ionization Energies

2020 ◽  
Author(s):  
Robson de Farias
Keyword(s):  
Quantum Mechanics ◽  
Relativistic Quantum ◽  
Empirical Method ◽  
Heavy Elements ◽  
Relativistic Quantum Mechanics ◽  
Ionization Energies ◽  
Semi Empirical ◽  
Good Agreement

<p>In the present work, it is shown that the first ionization energies for super-heavy elements (Z= 100-109) can be calculated by a semi-empirical method, if the super-heavy elements are treated (modelled) as calcium clusters. The values calculated in the present work are in good agreement compared with those from literature (modelling the super-heavy elements themselves, based on relativistic quantum mechanics). </p>

The molecular orbital theory of chemical valency VIII. A method of calculating ionization potentials

1951 ◽  
Vol 205 (1083) ◽  
pp. 541-552 ◽  
Keyword(s):  
Molecular Orbital ◽  
Empirical Method ◽  
Ionization Potentials ◽  
Orbital Method ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Atomic Orbitals ◽  
Usual Form ◽  
Semi Empirical ◽  
Good Agreement

An analysis of the ‘linear combination of atomic orbitals’ approximation using the accurate molecular orbital equations shows that it does not lead to equations of the form usually assumed in the semi-empirical molecular orbital method. A new semi-empirical method is proposed, therefore, in terms of equivalent orbitals. The equations obtained, which do have the usual form, are applicable to a large class of molecules and do not involve the approximations that were thought necessary. In this method the ionization potentials are calculated by treating certain integrals as semi-empirical parameters. The value of these parameters is discussed in terms of the localization of equivalent orbitals and some approximate rules are suggested. As an illustration the ionization potentials of the paraffin series are considered and good agreement between the observed and calculated values is found.

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