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The effect of ultraviolet lasers on conversion of methane into higher hydrocarbons
, Article Laser and Particle Beams ; Volume 31, Issue 3 , 2013 , Pages 481-486 ; 02630346 (ISSN) ; Irani, E ; Sadighi Bonabi, R ; Sharif University of Technology
2013
Abstract
Conversion of CH4 molecule into higher hydrocarbons using two different wavelengths of 248 nm KrF laser and 355 nm of third harmonic of Nd:YAG laser is studied experimentally and theoretically. The stable products are analyzed and the effect of pressure on conversion of methane is measured. The detected reaction products are C2H2, C2H4, and C2H6. The conversion efficiency of 33.5% for 355 nm in comparison to 2.2% conversion for 248 nm for C2H2 is achieved. The potential of laser parameters as an important variable in controlling of final products is investigated
Dissociation of C-H molecular bond of methane by pulse shaped ultra-intense laser field
, Article Chemical Physics Letters ; Volume 560 , 2013 , Pages 60-65 ; 00092614 (ISSN) ; Irani, E ; Navid, H. A ; Dehghani, Z ; Anvari, A ; Sadighi Bonabi, R ; Sharif University of Technology
2013
Abstract
The effects of laser field and laser pulse width on the dissociation probability of C-H bond of CH4 have been investigated. Calculation of time dependent Schrödinger equation by grid spectral method is carried out and it is produced optimistic results in comparison to the earlier Quasi-classical calculations. The results show that there is an excellent match with experimental data. In this work, a number of results in the emerging field of laser with intensity of I = 8 × 1013 W cm-2 and pulse duration of 100 fs are presented. The present modulated field leads to more than 20% improvement in the dissociation probability
Theoretical investigation on antioxidant activity of bromophenols from the marine red alga Rhodomela confervoides: H-atom vs electron transfer mechanism
, Article Journal of Agricultural and Food Chemistry ; Volume 61, Issue 7 , 2013 , Pages 1534-1541 ; 00218561 (ISSN) ; Javan, M. J ; Tehrani, Z. A ; Sharif University of Technology
2013
Abstract
Bromophenols are known as antioxidant radical scavengers for some biomolecules such as those in marine red alga. Full understanding of the role played by bromophenols requires detailed knowledge of the radical scavenging activities in probable pathways, a focus of ongoing research. To gain detailed insight into two suggested pathways, H-atom transfer and electron transfer, theoretical studies employing first principle quantum mechanical calculations have been carried out on selected bromophenols. Detailed investigation of the aforementioned routes revealed that upon H-atom abstraction or the electron transfer process, bromophenols cause an increase in radical species in which the unpaired...
The effect of intense short pulse laser shapes on generating of the optimum wakefield and dissociation of methane molecule
, Article Laser and Particle Beams ; Volume 30, Issue 3 , May , 2012 , Pages 357-367 ; 02630346 (ISSN) ; Zare, S ; Navid, H. A ; Dehghani, Z ; Sadighi Bonabi, R ; Sharif University of Technology
2012
Abstract
The optimum convolution of dual short pulse for producing the maximum wakefield and the highest dissociation probability of CH4 has been investigated. By using three fundamental shapes of pulses though four different arrangements, the generated wake are considered in plasma. It is found that when the first and second pulses were rectangular-triangular and sinusoidal pulse shapes, respectively, the resultant wakefield amplitude is the highest. This effect opens up a new novel way by pulse shaping mechanism in the photo dissociation dynamics of molecules and controlling of chemical reactions in the desired channels by short pulse intense lasers for reducing the computation time of genetic...
What roles do boron substitutions play in structural, tautomeric, base pairing and electronic properties of uracil? NBO & AIM analysis
, Article Journal of Physical Organic Chemistry ; Volume 25, Issue 9 , 2012 , Pages 787-796 ; 08943230 (ISSN) ; Abedin, A ; Shakourian Fard, M ; Fattahi, A ; Sharif University of Technology
Wiley
2012
Abstract
The synthesis of modified versions of deoxyribonucleic acid is an area that is receiving much attention. The replacement of the nitrogen atom on the nucleobases with boron atom has provided insight into deoxyribonucleic acid and ribonucleic acid stability, recognition, and replication at the atomic level. In the present research, we investigated a detailed density functional theory study of the structural, tautomeric, base-pairing ability, bond dissociation energy, and electronic properties of two boron analogues (i.e., boron substitutions at 4-position and 5-position of uracil) of uracil nucleobase. The effects of these modifications on theirs acid-base properties have been considered. Our...
Mechanisms and kinetics of Thiotepa and tepa hydrolysis: DFT study
, Article Journal of Molecular Modeling ; Volume 18, Issue 8 , 2012 , Pages 3563-3576 ; 16102940 (ISSN) ; Fattahi, A ; Sharif University of Technology
Springer
2012
Abstract
N,N′,N″-triethylenethiophosphoramide (Thiotepa) and its oxo analogue (Tepa) as the major metabolite are trifunctional alkylating agents with a broad spectrum of antitumor activity. In vivo and vitro studies show alkylation of DNA by Thiotepa and Tepa can follow two pathways, but it remains unclear which pathway represents the precise mechanism of action. In pathway 1, these agents are capable of forming cross-links with DNA molecules via two different mechanisms. In the first mechanism, the ring opening reaction is initiated by protonating the aziridine, which then becomes the primary target of nucleophilic attack by the N7-Guanine. The second one is a direct nucleophilic ring opening of...
First principles study of oxygen adsorption on nickel-doped graphite
, Article Molecular Physics ; Volume 110, Issue 13 , Feb , 2012 , Pages 1437-1445 ; 00268976 (ISSN) ; Gobal, F ; Sharif University of Technology
2012
Abstract
Density functional theory is used in a spin-polarized plane wave pseudopotential implementation to investigate molecular oxygen adsorption and dissociation on graphite and nickel-doped graphite surfaces. Molecular oxygen physisorbs on graphite surface retaining its magnetic property. The calculated adsorption energy is consistent with the experimental value of 0.1eV. It is found that substituting a carbon atom of the graphite surface by a single doping nickel atom (2.8% content) makes the surface active for oxygen chemisorption. It is found that the molecular oxygen never adsorbs on doping nickel atom while it adsorbs and dissociates spontaneously into atomic oxygens on the carbon atoms...
Adsorption and dissociation of hydrogen peroxide on small Pd xM3-x (M = Pt, Cu; X = 1-3) clusters: A hybrid density functional study
, Article Molecular Physics ; Volume 109, Issue 14 , May , 2011 , Pages 1797-1804 ; 00268976 (ISSN) ; Gobal, F ; Arab, R ; Sharif University of Technology
2011
Abstract
The adsorption and dissociation of H2O2 on small PdxM3-x (M=Pt, Cu; x = 1-3) clusters is investigated using the B3PW91 hybrid density functional method. Natural bond orbitals are analysed to obtain partial charges on atoms, dipole moments, bond orders, and hybrid orbitals of the PdxM3-x-H2O2 systems. The calculated adsorption energies are in the range of -0.32 to -2.12 eV. Generally, H2O2 adsorbs on top positions through one of its oxygen atoms and only in a few cases reacts with the cluster through both oxygen and hydrogen sides. In the latter case the cluster sites which are negatively charged interact with the hydrogen atoms. Interestingly, on the triplet Pd2Pt cluster, H2O2 dissociates...
Optimization of two tailored rectangular femtosecond laser pulses in methane dissociation
, Article Proceedings of SPIE - The International Society for Optical Engineering, 12 April 2010 through 16 April 2010 ; Volume 7721 , April , 2010 ; 0277786X (ISSN) ; 9780819481948 (ISBN) ; Dehghani, Z ; Irani, E ; The Society of Photo-Optical Instrumentation Engineers (SPIE); Brussels Photonics Team (B-PHOT); Brussels-Capital Region; Fonds Wetenschappelijk Onderzoek (FWO); International Commission for Optics (ICO) ; Sharif University of Technology
2010
Abstract
Based on the quantum mechanics principles and classically calculated dressed potential surfaces by using field assisted dissociation model the dissociation probability for CH4 + molecule exposed with a 100 femtosecond 8 Jcm-2 Ti:sapphire laser pulses is calculated. Using the gradient optimization method two tailored rectangular laser pulses for controlling the dissociation of C-H bond of CH4 + molecule along laser pulse direction is found. In the proposed optimization method, the complicacy of solving Schrodinger wave equation is reduced by using classical method and in contrast to the usual controlling and pulse shaping methods of chemical reactions, the experimental data is not needed and...
Extraordinary swelling behavior of poly (AMPS) organogelin solvent/DMSO binary mixed media
, Article Journal of Applied Polymer Science ; Volume 117, Issue 2 , July , 2010 , Pages 1127-1136 ; 00218995 (ISSN) ; Kabiri, K ; Kheirabadi, M ; Sharif University of Technology
2010
Abstract
The present article deals with super-swelling behavior of crosslinked homopolymer of 2-acrylamido-2-methylpropane sulfonic acid, poly(AMPS), in binary mixtures of dimethyl sulfoxide (DMSO) and various polar solvents including water, mono-, and polyhydric alcohols, and amide solvents such as N-methyl pyrrolidone. Extraordinary phase transition sequences including a new unusual swelling phenomenon, referred to as "overentrant" swelling, was observed for this polymeric organogel in the solvent/DMSO mixtures. The swelling behaviors were preliminarily explained based on the major interactions involved in the solvation process and dielectric constant of the swelling media. It was established that...
Recent results of edge plasma parameters measurements in IR-T1 tokamak by probe
, Article Journal of Fusion Energy ; Volume 29, Issue 3 , June , 2010 , Pages 271-274 ; 01640313 (ISSN) ; Emami, M ; Ghoranneviss, M ; Abaspour Tehrani Fard, A ; Sharif University of Technology
2010
Abstract
Langmuir probes (LP) are the most common diagnostics for the local measurement of very important plasma parameters such as plasma density, electron temperature, plasma potential and the electron energy distribution function (EEDF). In this paper the applicability of the first derivative Langmuir probe method in processing the electron part of the current-voltage (I-V) characteristics in IR-T1 Tokamak is reported. The EEDF at different radial positions in the edge region and Scrape off Layer (SOL) are derived and the values of the plasma potential, electron temperature and electron density are estimated. Results comparison between the first derivative method and Stangeby method shows a...
Adsorption of carbon monoxide on SixGe4-x(x = 0-4) nano-clusters: A hybrid meta density functional study
, Article Molecular Physics ; Volume 108, Issue 10 , 2010 , Pages 1317-1327 ; 00268976 (ISSN) ; Gobal, F ; Sharif University of Technology
2010
Abstract
Theoretical study of carbon monoxide adsorption on SixGe4 - x(x = 0-4) nano-clusters has been carried out using advanced hybrid meta density functional method of Truhlar (MPW1B95). MG3 semi-diffuse (MG3S) and correlation consistent valence basis sets with relativistic core potential were employed to improve the results. The agreement of the calculated ionization and dissociation energies with experimental values validates the reported structures of nano-clusters and justifies the use of hybrid meta density functional method. The geometry, adsorption energy, charge distribution, and vibrational frequency of CO adsorption on all possible structures were investigated. The maximum vibrational...
Origin of the correlation of the rate constant of substrate hydroxylation by nonheme iron(IV)-oxo complexes with the bond-dissociation energy of the C-H bond of the substrate
, Article Chemistry - A European Journal ; Volume 15, Issue 27 , 2009 , Pages 6651-6662 ; 09476539 (ISSN) ; Bagherzadeh, M ; De Visser, S ; Sharif University of Technology
Wiley-VCH Verlag
2009
Abstract
Mononuclear nonheme iron containing systems are versatile and vital oxidants of substrate hydroxylation reactions in many biosystems, whereby the rate constant of hydroxylation correlates with the strength of the C-H bond that is broken in the process. The thermodynamic reason behind these correlations, however, has never been established. In this work results of a series of density functional theory calculations of substrate hydroxylation by a mononuclear nonheme iron(IV)-oxo oxidant with a 2 His/ 1Asp structural motif analogous to aketoglutarate dependent dioxygenases are presented. The calculations show that these oxidants are very efficient and able to hydroxylate strong C-H bonds,...
Conversion of a weak organic acid to a super acid in the gas phase
, Article Journal of Physical Organic Chemistry ; Volume 21, Issue 2 , 2008 , Pages 112-118 ; 08943230 (ISSN) ; Tavasoli, E ; Sharif University of Technology
2008
Abstract
The effects of selected metal ions on the gas-phase acidity of weak organic acids have been explored using the DFT and Moller-Plesset Perturbation Theory (MP2) calculations. The three organic acids selected for this study were acetic acid (aliphatic), benzoic acid (aromatic), and glycine (amino acid). The acidities of these compounds are compared with the acidity of their Li +-, Na+-, and K+ -complexed species. The results indicate that upon complexation with Li+, Na+, and K+ at 298K, the gas-phase acidity of acetic acid, for example, varies from 345.3 to 218.8, 230.2, and 240.1 kcal/mol, respectively (i.e., its dissociation becomes much less endothermic). These values indicate that a weak...
Carbon dioxide reforming of methane by pulsed glow discharge at atmospheric pressure: the effect of pulse compression
, Article Journal of Applied Physics ; Volume 101, Issue 12 , 2007 ; 00218979 (ISSN) ; Modarresi, H ; Sharif University of Technology
2007
Abstract
Methane reforming by carbon dioxide in pulsed glow discharge at atmospheric pressure is examined. The plasma pulse is compressed to less than 50 ns. This compression enables one to work at higher frequencies, over 3 kHz, without glow-arc transition. The main products of the reaction are synthetic gases (H2, CO) and C2 hydrocarbons. Approximately 42% of plasma energy goes to the chemical dissociation, when the reactant ratio is C O2 C H4 =1. At this point, the energy expense is less than 3.8 eV per converted molecule while reactant conversions are relatively high reaching to 55% (C H4) and 42% (C O2). The reactor energy performance even gets better at higher C O2 C H4 ratios. While energy...
High energy efficiency in syngas and hydrocarbon production from dissociation of CH4-CO2 mixture in a non-equilibrium pulsed plasma
, Article Journal of Physics D: Applied Physics ; Volume 38, Issue 20 , 2005 , Pages 3804-3811 ; 00223727 (ISSN) ; Norouzi, S ; Mohammadi, T ; Sharif University of Technology
2005
Abstract
The efficient production of syngas from a CH4+CO2 mixture in an atmospheric pulsed glow discharge, sustained by corona pre-ionization, has been investigated. The products were mainly syngas (CO, H2) and hydrocarbons up to C4, with acetylene having the highest selectivity. The energy efficiency was within 15-40% for different experimental conditions, which demonstrates a comprehensive improvement relative to the achievements of other types of non-equilibrium plasma. These values are, however, comparable with the efficiencies obtained by gliding arc plasmas but this plasma operates at near room temperature. Furthermore, it has been shown that the energy efficiency is increased by decreasing...
Modified carrageenan. 1. H-CarragPAM, a novel biopolymer-based superabsorbent hydrogel
, Article Journal of Bioactive and Compatible Polymers ; Volume 20, Issue 5 , 2005 , Pages 475-490 ; 08839115 (ISSN) ; Pourjavadi, A ; Mahdavinia, G. R ; Zohuriaan Mehr, M. J ; Sharif University of Technology
2005
Abstract
A novel kappa-carrageenan (κC)-based superabsorbing hydrogel was synthesized through graft copolymerization of acrylamide (AAm) onto a κC substrate in the presence of a crosslinking agent. The crosslinked κC-poly(AAm) polymer graft was partially hydrolyzed in alkaline medium to yield a superabsorbent resin, H-carragPAM. The resin structure was confirmed using FTIR spectroscopy. The variables of graft copolymerization (monomer, initiator, polysaccharide and crosslinker concentration, reaction temperature and time as well as stirrer speed) that affected on the ultimate water-swelling capacity were optimized. The time-temperature variation of the copolymerization was investigated in terms of...
Methane conversion to hydrogen and higher hydrocarbons by double pulsed glow discharge
, Article Plasma Chemistry and Plasma Processing ; Volume 25, Issue 1 , 2005 , Pages 19-29 ; 02724324 (ISSN) ; Matin, N. S ; Sharif University of Technology
2005
Abstract
Pulsed atmospheric glow plasma, sustained by corona discharge, was utilized to convert methane. Analysis by gas chromatography showed that hydrogen and C2-products are the main constituents of outlet mixture while C 2+-products with small concentrations were also detected. The chemical energy efficiency turned out to be about 9% for the best result obtained by this type of reactor. It has been shown that more improvement of energy efficiency is possible by increasing ' the pulse repetition rate
Mechanism of catalytic decomposition of CH3I on the Cu(111) surface: A UBI-QEP approach
, Article Langmuir, Washington, DC, United States ; Volume 16, Issue 21 , 2000 , Pages 8095-8099 ; 07437463 (ISSN) ; Gobal, F ; Sharif University of Technology
ACS
2000
Abstract
The method of unity bond index-quadratic exponential potential (UBI-QEP) and the computer simulation of the temperature programmed desorption (TPD) patterns are employed to derive the kinetic and thermodynamic parameters associated with the steps of the pathway we propose for the catalytic decomposition of methyl iodide on the Cu(111) surface. Assuming a highly reactive `hot methyl' surface intermediate and on the basis of our calculations it is concluded that the desorption of a part of this species is responsible for the reported methyl radical TPD peak at 140 K, while a part of this surface species is trapped in the three-fold sites of the Cu(111) surface and desorbs to form the reported...
Molecular Dynamics Study in the Interaction of Intense Femtosecond Laser Pulse with Methane Molecule
, Ph.D. Dissertation Sharif University of Technology ; Sadighi-Bonabi, Rasul (Supervisor) ; Anvari, Abbas (Co-Advisor) ; Asgari, Reza (Co-Advisor)
Abstract
In this project, the ionization and dissociation of methane molecule by intense femto-second lasers has been studied. Dissociation probability is calculated for interacting CH4 molecule under Ti: Sapphire laser pulse with pulse durations of 10- 40fs in intensities at the range of 1014-1016 Wcm-2. Calculations are carried out with time-dependent density functional theory using Gaussian03 and Octopus packages as powerful computational chemical physics programs. Due to importance of the dependence of interaction dynamics to laser parameters, the effect of these parameters including different intensities, polarization, various pulse durations and pulse envelopes are investigated. The optimal...