Supersonically expanding reacting flows : the chemiluminescent Sn/N2O reaction

1981 ◽  
Vol 34 (2) ◽  
pp. 271
Author(s):  
JC Mackie ◽  
J Nicholls
Keyword(s):  
Activation Energy ◽  
Nitrous Oxide ◽  
Supersonic Flow ◽  
Excited States ◽  
Flow Reactor ◽  
Kinetic Modelling ◽  
Branching Ratios ◽  
Reacting Flows ◽  
Chemiluminescent Reaction ◽  
Electronic Chemical

A supersonic flow reactor comprising a shock tube and convergent-divergent expansion nozzle has been developed and used to study the chemiluminescent reaction between tin atoms and nitrous oxide. The reaction has been found to excite the a-X, b-X and A-X transitions of SnO and rate constants for formation of the three excited states have been found to have the same activation energy, 25�5 kJ mol-1. Estimates of branching ratios have been made on the basis of experimental measurement and kinetic modelling and an assessment of the Sn/N2O reaction as a possible electronic chemical laser is made.

Relevance of the Entropy Factor in Stereoselectivity Control of Asymmetric Photoreactions

Synlett ◽  
2020 ◽  
Vol 31 (13) ◽  
pp. 1259-1267
Author(s):  
Tadashi Mori
Keyword(s):  
Activation Energy ◽  
Excited States ◽  
Weak Interactions ◽  
Supramolecular Interactions ◽  
Thermal Reactions ◽  
Thermodynamics And Kinetics ◽  
Control Concept ◽  
Entropy Factor ◽  
Fine Tune

Entropy as well as enthalpy factors play substantial roles in various chemical phenomena such as equilibrium and reactions. However, the entropy factors are frequently underestimated in most instances, particularly in synthetic chemistry. In reality, the entropy factor can be in competition with the enthalpy factor or can even be decisive in determining the overall free or activation energy change upon molecular interaction and chemical transformation, particularly where weak interactions in ground and/or excited states are significant. In this account, we overview the importance of the entropy factor in various chemical phenomena in both thermodynamics and kinetics and in the ground and excited states. It is immediately apparent that many diastereo- and enantioselective photoreactions are entropy-controlled. Recent advances on the entropy-control concept in asymmetric photoreactions are further discussed. Understanding the entropy-control concept will pave the way to improve, fine-tune, and even invert the chemo- and stereoselectivity of relevant chemical phenomena.1 Introduction2 Role of Entropy in Supramolecular Interactions3 Selected Examples of Entropy-Driven Thermal Reactions4 Classical Examples of Entropy Control in Photoreactions5 Entropy-Driven Asymmetric Photoreactions6 Advances in Entropy Control7 Perspective

Branching ratios in the radiative decay of helium doubly excited states

2005 ◽  
Vol 72 (5) ◽  
Author(s):  
M. Coreno ◽  
K. C. Prince ◽  
R. Richter ◽  
M. de Simone ◽  
K. Bučar ◽  
...  
Keyword(s):  
Excited States ◽  
Radiative Decay ◽  
Branching Ratios ◽  
Doubly Excited States ◽  
Doubly Excited

scholarly journals The thermal decomposition of nitrous oxide at pressures up to forty atmospheres

1934 ◽  
Vol 144 (852) ◽  
pp. 386-412 ◽  
Keyword(s):  
Activation Energy ◽  
Nitrous Oxide ◽  
Atmospheric Pressure ◽  
Initial Pressure ◽  
Bimolecular Reaction ◽  
Absolute Temperature ◽  
Velocity Constant ◽  
A Value ◽  
Straight Line ◽  
Rate Of Reaction

Nitrous oxide decomposes to nitrogen and oxygen at velocities which can be conveniently measured at temperatures between 600° and 850° C. M. A. Hunter investigated the reaction by streaming the gas through a porcelain bulb in a furnace and measuring the decomposition for different times of passage. No attempt was made to determine whether the reaction is homogeneous or heterogeneous. The effect of wide variation of pressure was not used to determine its order, since the reaction was followed only over small ranges of decomposition at atmospheric pressure. From the velocity of decomposition, however, bimolecular constants were obtained which could be represented by the equation: ln k = 24·12 - 31800/T, where k is the bimolecular velocity constant and T the absolute temperature. If this equation holds, the activation energy of the bimolecular reaction is 62,040 cal./gm. mol. A much more thorough examination of the reaction was made by Hinshelwood and Burk, who measured the rate of reaction by following the pressure increase at constant volume in a silica bulb. The reaction was proved to be homogeneous. The initial pressure was varied between 50 and 500 mm. Hg, and it was found that the reciprocal of the half-lives when plotted against the initial pressures gave a straight line. true bimolecular reaction requires the straight line 1/ t ½ = ka , where t ½ is the half-line, and k the velocity constant, and a the initial concentration. The line through the experimental points showed a small intercept on the 1/ t ½ axis for which no explanation was offered at the time. From the variation of the bimolecular constants between 565° and 852° C. the activation energy of the reaction was calculated to be 58,450 cal./gm. mol. If the reaction were a bimolecular one dependent on immediate decomposition at each activating collision of the molecules the number of molecules reacting per second should be equal to Z x e -E/RT , where Z is the number of molecules colliding per second and E is the activation energy. From the observed rate of reaction at 1000° K. a value of 55,000 cal./gm. mol. was found for the activation energy. The fairly close agreement between the two values of the activation energy, 58,450 and 55,000 cal./gm. mol. and the manner in which the half-life varied with pressure provided good grounds for believing the reaction to be a simple bimolecular one, dependent only on collisions between the molecules.

Electrical, Optical, Structural, and Analytical Properties of Very Pure GaN

2002 ◽  
Vol 743 ◽  
Author(s):  
D. C. Look ◽  
J. R. Sizelove ◽  
J. Jasinski ◽  
Z. Liliental-Weber ◽  
K. Saarinen ◽  
...  
Keyword(s):  
Activation Energy ◽  
Hall Effect ◽  
Excited States ◽  
Vacancy Concentration ◽  
Strong Line ◽  
Threading Dislocation ◽  
Charge Balance ◽  
Acceptor Concentration ◽  
Flat Surfaces ◽  
The Difference

ABSTRACTPresent hydride vapor phase epitaxial growth of GaN on Al2O3 can produce material of very high quality, especially in regions of the crystal far from the substrate/epilayer interface. In the present study, we characterize a 248-μm-thick epilayer, which had been separated from its Al2O3 substrate and etched on top and bottom to produce flat surfaces. Temperature-dependent Hall-effect data have been fitted to give the following parameters: mobility μ(300) = 1320 cm2/V-s; μ(peak) = 12,000 cm2/V-s; carrier concentration n(300) = 6.27 × 1015 cm−3; donor concentration ND = 7.8 × 1015 cm−3; acceptor concentration NA = 1.3 × 1015 cm−3; and effective donor activation energy ED = 28.1 meV. These mobilities are the highest ever reported in GaN, and the acceptor concentration, the lowest. Positron annihilation measurements give a Ga vacancy concentration very close to NA, showing that the dominant acceptors are likely native defects. Secondary ion mass spectroscopic measurements show that ND is probably composed of the common donors O and Si, with [O] > [S1]. Transmission electron microscopy measurements yield threading dislocation densities of about 1 × 107 cm−2 on the bottom (N) face, and < 5 × 105 cm−2 on the top (Ga) face. Photoluminescence (PL) spectra show a strong donor-bound exciton (D°X) line at 3.47225 eV, and a weaker one at 3.47305 eV; each has a linewidth of about 0.4 meV. In the two-electron satellite region, a strong line appears at 3.44686 eV, and a weaker one at 3.44792 eV. If the two strong lines represent the same donor, then ED,n=1 – ED,n=2 = 25.4 meV for that donor, and the ground-state activation energy (EC – ED,n=1) is (4/3)25.4 = 33.9 meV in a hydrogenic model, and 32.7 meV in a somewhat modified model. The measured Hall-effect donor energy, 28.1 meV, is smaller than the PL donor energy, as is nearly always found in semiconductors. We show that the difference in the Hall and PL donor energies can be explained by donor-band conduction via overlapping donor excited states, and the effects of non-overlapping excited states which should be included in the n vs. T data analysis (charge balance equation).

Going beyond the three-state ensemble model: the electronic chemical potential and Fukui function for the general case

2017 ◽  
Vol 19 (18) ◽  
pp. 11588-11602 ◽  
Author(s):  
Marco Franco-Pérez ◽  
Farnaz Heidar-Zadeh ◽  
Paul W. Ayers ◽  
José L. Gázquez ◽  
Alberto Vela
Keyword(s):  
Excited States ◽  
Chemical Potential ◽  
Fukui Function ◽  
Ensemble Model ◽  
State Ensemble ◽  
Electronic Chemical Potential ◽  
Electronic Chemical

The analytical working equations for the chemical potential and the Fukui function for the case of any number of ground and excited states is presented.

Hydrogen–nitrous oxide delay times: Shock tube experimental study and kinetic modelling

2009 ◽  
Vol 32 (1) ◽  
pp. 359-366 ◽  
Author(s):  
R. Mével ◽  
S. Javoy ◽  
F. Lafosse ◽  
N. Chaumeix ◽  
G. Dupré ◽  
...  
Keyword(s):  
Experimental Study ◽  
Nitrous Oxide ◽  
Shock Tube ◽  
Kinetic Modelling ◽  
Delay Times

scholarly journals Pyrolysis kinetic modelling of abundant plastic waste (PET) and in-situ emissions monitoring

2020 ◽  
Author(s):  
Ahmed I. Osman ◽  
Charlie Farrell ◽  
Ala'a H. Al-Muhtaseb ◽  
Ahmed S. Al-Fatesh ◽  
John Harrison ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Activation Energy ◽  
Kinetic Modelling ◽  
Degradation Mechanism ◽  
Scale Up ◽  
Plastic Waste ◽  
Gaseous Emissions ◽  
Low Carbon ◽  
Pyrolysis Process

Abstract Background: Recycling the ever-increasing plastic waste has become an urgent global concern. One of the most convenient methods for plastic recycling is pyrolysis, owing to its environmentally friendly nature and its intrinsic properties. Understanding the pyrolysis process and the degradation mechanism is crucial for scale-up and reactor design. Therefore, we studied kinetic modelling of the pyrolysis process for one of the most common plastics, polyethylene terephthalate (PET). The focus was to better understand and predict PET pyrolysis when transitioning to a low carbon economy and adhering to environmental and governmental legislation. This work aims at presenting for the first time, the kinetic triplet (activation energy, pre-exponential constant and reaction rate) for the PET pyrolysis using the differential iso-conversional method. This is coupled with the in-situ online tracking of the gaseous emissions using mass spectrometry.Results: The differential iso-conversional method showed activation energy (Ea) values of 165-195 kJ.mol-1, R2 = 0.99659. While the ASTM-E698 showed 165.6 kJ.mol-1 and integral methods such as Flynn-Wall and Ozawa (FWO) (166-180 kJ.mol-1). The in-situ Mass Spectrometry results showed the pyrolysis gaseous emissions which are C1-hydrocarbon and H-O-C=O along with C2 hydrocarbons, C5- C6 hydrocarbons, acetaldehyde, the fragment of O-CH=CH2, hydrogen and water. Conclusions: From the obtained results herein, thermal predictions (isothermal, non-isothermal and step-based heating) were determined based on the kinetic parameters and can be used at numerous scales with a high level of accuracy compared with the literature.

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