Copper Corrosion Mechanisms of Polysulfides

1997 ◽  
Vol 492 ◽  
Author(s):  
Anne M. Chaka ◽  
John Harris ◽  
X. P. Li
Keyword(s):  
Density Functional ◽  
Copper Surface ◽  
Minor Role ◽  
Copper Corrosion ◽  
Dramatic Decrease ◽  
Functional Theory ◽  
Hartree Fock ◽  
Thiyl Radicals ◽  
Corrosion Mechanisms ◽  
A Minor

ABSTRACTCorrosive behavior of commercial organopolysulfides of the type R-(S)n-R is known to increase dramatically towards copper-based alloys when n ≥ 4, whereas di- and trisulfides are essentially inert. Three possible reasons for this behavior are examined using local and nonlocal density-functional theory as well as post-Hartree-Fock theory at the MP2 level. The hypotheses are: the shorter chains are protected from the surface by steric hindrance of the terminal organic groups, longer polysulfides can chelate copper atoms and remove them from the surface, and S-S bonds become weaker and more reactive as the polysulfide chains become longer. We find the predominant reason for the increase in corrosive behavior to be a dramatic decrease in S-S bond dissociation energy when n ≥ 4 due to stabilization of the unpaired electron via delocalization in RSS• thiyl radicals. The thiyl radicals are thus the species which is capable of attacking and corroding the copper surface. Chelation is eliminated as a possible mechanism, and steric protection and oil solubility afforded by the organic terminal groups are found to play a minor role.

Enhanced and Retarded Diffusion of Shallow Impurities in Silicon

1988 ◽  
Vol 141 ◽  
Author(s):  
C.S. Nichols ◽  
C. G. Van De Walle ◽  
S.T. Pantelides
Keyword(s):  
Density Functional ◽  
Activation Energies ◽  
Minor Role ◽  
Functional Theory ◽  
Interstitial Component ◽  
Equilibrium Concentrations ◽  
Diffusion Mechanisms ◽  
Shallow Impurities ◽  
A Minor ◽  
Non Equilibrium

AbstractWe have carried out systematic state-of-the-art calculations using density-functional theory, norm-conserving pseudopotentials, and large supercells in order to investigate the diffusion mechanisms of B, P, As, and Sb in Si under both equilibrium and non-equilibrium concentrations of intrinsic point defects. In addition, we have developed a theory for the non-equilibrium concentrations of the relevant diffusing species from which expressions for the activation energies may be derived. In equilibrium, we find that vacancies and self-interstitials mediate the diffusion of B, P, and As with comparable activation energies, but we show from our non-equilibrium diffusion calculations that these impurities have a dominant interstitial component. Sb diffusion, on the other hand, is mediated primarily by vacancies. We also find that the direct exchange mechanism plays only a minor role in all cases.

scholarly journals Ring carbo-mers: From questionable homoaromaticity to bench aromaticity

2006 ◽  
Vol 78 (4) ◽  
pp. 791-811 ◽  
Author(s):  
Chunhai Zou ◽  
Christine Lepetit ◽  
Yannick Coppel ◽  
Remi Chauvin
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Minor Role ◽  
Electron Localization ◽  
Functional Theory ◽  
Parent Molecule ◽  
Vis Spectroscopy ◽  
The Stability ◽  
A Minor ◽  
Theory And Experiment

The title journey is undertaken at the levels of both theory and experiment. Since 1983, homoaromaticity has been shown to play at most a minor role in the stability of Scott's [N]pericyclyne hydrocarbons - the first ring carbo-mers of cycloalkanes. This statement has been systematically refined for N = 3-6 by using both classical theoretical tools and newly designed tools based on electron localization function (ELF) analysis. The compatibility of the [5]- and [6]-pericyclyne cores with vertex functionalities was established by the synthesis of 20 oxy (carbo-cyclitol) derivatives. The stereoisomeric resolution of two of them has been achieved. Hexaoxy-[6]pericyclynes are actually potential precursors of the carbo-benzenes. Criteria based on density functional theory (DFT) calculations (magnetic, energetic, structural/"electronic") show that the aromaticity of carbo-[N]annulenic species is comparable to that of their parent molecule. This has been challenged by the synthesis of several novel carbo-benzenic molecules with various substitution patterns. The theory-experiment interplay is pursued by considering ring carbo-mers of other conjugated ring systems such as radialenes. The second carbo-mers (butadiyndiyl-expanded rings) of [3]radialene and benzene are also envisioned. Hexaphenyl-carbo2-benzene has been observed by 1H and UV-vis spectroscopy.

scholarly journals Unraveling the electrochemical and spectroscopic properties of neutral and negatively charged perylene tetraethylesters

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Christian Wiebeler ◽  
Joachim Vollbrecht ◽  
Adam Neuba ◽  
Heinz-Siegfried Kitzerow ◽  
Stefan Schumacher
Keyword(s):  
Absorption Spectra ◽  
Density Functional ◽  
Energy Levels ◽  
Spectroscopic Properties ◽  
Absorption Bands ◽  
Functional Theory ◽  
Vertical Excitation ◽  
Hartree Fock ◽  
Tauc Plot ◽  
Electrochemical Approach

AbstractA detailed investigation of the energy levels of perylene-3,4,9,10-tetracarboxylic tetraethylester as a representative compound for the whole family of perylene esters was performed. It was revealed via electrochemical measurements that one oxidation and two reductions take place. The bandgaps determined via the electrochemical approach are in good agreement with the optical bandgap obtained from the absorption spectra via a Tauc plot. In addition, absorption spectra in dependence of the electrochemical potential were the basis for extensive quantum-chemical calculations of the neutral, monoanionic, and dianionic molecules. For this purpose, calculations based on density functional theory were compared with post-Hartree–Fock methods and the CAM-B3LYP functional proved to be the most reliable choice for the calculation of absorption spectra. Furthermore, spectral features found experimentally could be reproduced with vibronic calculations and allowed to understand their origins. In particular, the two lowest energy absorption bands of the anion are not caused by absorption of two distinct electronic states, which might have been expected from vertical excitation calculations, but both states exhibit a strong vibronic progression resulting in contributions to both bands.

Polaronic and Bipolaronic Enhancement of Second Hyperpolarizabilities in Dithienyl Polyenes from Ab Initio Quantum Methods

1999 ◽  
Vol 597 ◽  
Author(s):  
Steven Trohalaki ◽  
Robert J. Zellmer ◽  
Ruth Pachter
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Valence Bond ◽  
Closed Shell ◽  
Functional Theory ◽  
Molecular Conformations ◽  
Hartree Fock ◽  
Molecular Charge ◽  
Field Methodology ◽  
Moller Plesset

AbstractSpangler and He [1,2] have shown that dithienyl polyenes form extremely stable bipolaronic dications when oxidatively doped in solution. Previous theoretical studies applied empirical methods to predict bipolaronic enhancement of hyperpolarizabilities for simple polyenes [3,4]. Here, we employ density functional theory to optimize the gas-phase molecular conformations of neutral, cationic, and dicationic forms of a series of dithienyl polyenes, where the number of ethene units, N, is varied from 1–5. Ab initio Hartree-Fock, generalized valence bond, configuration interaction, and Møller-Plesset calculations demonstrate that the dications are farily well described with a closed shell and therefore have little biradicaloid character. Second hyperpolarizabilities, γ, are subsequently calculated using ab initio Hartree-Fock theory and a finite field methodology. As expected, γ increases with the number of ethene units for a given molecular charge. The cations also show the largest increase in γ with N. For a given value of N, the cations display the largest γ values. However, if we treat the dication as a triplet, which might be present in solution, then it displays the largest γ.

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