State‐to‐state rate constants for quenching of xenon 6p levels by rare gases

1992 ◽  
Vol 96 (6) ◽  
pp. 4330-4340 ◽  
Author(s):  
W. J. Alford
Keyword(s):  
Rate Constants ◽  
Rare Gases ◽  
State Rate

The decomposition of aliphatic N-nitro amines in aqueous sulfuric acid. Bisulfate as a nucleophile

1996 ◽  
Vol 74 (10) ◽  
pp. 1774-1778 ◽  
Author(s):  
Robin A. Cox
Keyword(s):  
Sulfuric Acid ◽  
Water Molecule ◽  
Rate Constants ◽  
Activation Parameters ◽  
Standard State ◽  
Aqueous Sulfuric Acid ◽  
Alkyl Groups ◽  
Different Temperatures ◽  
State Rate ◽  
Acid Catalyzed

In aqueous sulfuric acid, aliphatic N-nitro amines decompose to N2O and alcohols. An excess acidity analysis of the observed rate constants for the reaction shows that free carbocations are not formed. The reaction is an acid-catalyzed SN2 displacement from the protonated aci-nitro tautomer, the nucleophile being a water molecule at acidities below 82–85% H2SO4, and a bisulfate ion at higher acidities. Bisulfate is the poorer nucleophile by a factor of about 1000. Twelve compounds were studied, of which results obtained for nine at several different temperatures enabled calculation of activation parameters for both nucleophiles. The reaction appears to be mainly enthalpy controlled. The intercept standard-state rate constants are well correlated by the σ* values for the alkyl groups; the slopes are negative, with a more negative value for the slower bisulfate reaction. Interestingly the m≠m* slopes also correlate with σ*, although the scatter is bad. Key words: N-nitro amines, excess acidity, bisulfate, nucleophiles, acid-catalyzed, kinetics.

scholarly journals Experimental and theoretical determination of rotational-translational state-to-state rate constants for N2:He collisions at low temperature (3

2003 ◽  
Vol 118 (10) ◽  
pp. 4477-4486 ◽  
Author(s):  
B. Maté ◽  
F. Thibault ◽  
A. Ramos ◽  
G. Tejeda ◽  
J. M. Fernández ◽  
...  
Keyword(s):  
Low Temperature ◽  
Rate Constants ◽  
Theoretical Determination ◽  
State Rate

Substituent effects on homolytic versus heterolytic photocleavage of (1-naphthylmethyl)trimethylammonium chlorides

1987 ◽  
Vol 65 (7) ◽  
pp. 1599-1607 ◽  
Author(s):  
B. Foster ◽  
B. Gaillard ◽  
N. Mathur ◽  
A. L. Pincock ◽  
J. A. Pincock ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Hydrogen Atom ◽  
Charge Distribution ◽  
Rate Constants ◽  
Bond Cleavage ◽  
Substituent Effects ◽  
Hydrogen Atom Transfer ◽  
Singlet Excited State ◽  
State Rate

Singlet excited state rate constants have been measured for both the heterolytic and homolytic photocleavage of 3- and 4-methoxy and 3- and 4-cyano (1-naphthylmethyl)trimethylammonium chlorides, 6–10. The results are interpreted in terms of the meta effect or changes in charge distribution upon excitation and the competition between bond cleavage, electron transfer, and hydrogen atom transfer in the contact pairs resulting from the two types of cleavage.

Effect of the potential-energy surface on the diatom dissociation rate constant for F 2 in Ar at 3000 K

1987 ◽  
Vol 414 (1847) ◽  
pp. 297-314
Keyword(s):  
Steady State ◽  
Rate Constant ◽  
Rate Constants ◽  
Reaction Rate ◽  
Energy Surface ◽  
Rate Coefficient ◽  
Classical Mechanics ◽  
Rate Coefficients ◽  
Steady State Rate ◽  
State Rate

Gas-phase dissociation of fluorine ( 1 Ʃ + g ) molecules in an agron bath at 3000 K was studied by using the 3D Monte Carlo classical trajectory (3DMCCT) method. To assess the importance of the potential energy surface (PES) in such calculations, three surfaces, with a fixed, experimentally determined F 2 dissociation energy, were constructed. These surfaces span the existing experimental uncertainties in the shape of the F 2 potential. The first potential was the widest and softest; in the second potential the anharmonicity was minimized. The intermediate potential was constructed to ‘localize’ anharmonicity in the energy range in which the collisions are most reactive. The remaining parameters for each PES were estimated from the best available data on interatomic potentials. By using the single uniform ensemble (SUE) method (Kutz, H. D. & Burns, G. J. chem. Phys . 72, 3652-3657 (1980)), large ensembles of trajectories (LET) were generated for the PES. Two such ensembles consisted of 30000 trajectories each and the third of 26200. It was found that the computed one-way-flux equilibrium rate coefficients (Widom, B. Science 148, 1555-1560 (1965)) depend in a systematic way upon the anharmonicity of the potential, with the most anharmonic potential yielding the largest rate coefficient. Steady-state reaction-rate constants, which correspond to experimentally observable rate constants, were calculated by the SUE method. It was determined that this method yields (for a given trajectory ensemble, PES and translational temperature) a unique steady-state rate constant, independent of the initial, arbitrarily chosen, state (Tolman, R. C. The principles of statistical mechanics , p. 17. Oxford University Press (1938)) of the LET, and consequently independent of the corresponding initial value of the reaction rate coefficient. For each initial state of the LET, the development of the steady-state rate constant from the equilibrium rate coefficient was smooth, monotonic, and consistent with the detailed properties of the PES. It was found that, although the increased anharmonicity of the F 2 potential enhanced the equilibrium rate coefficients, it also enhanced the non-equilibrium effects. As a result, the steady-state rate constants were found to be insensitive to the variation of the PES. Thus, the differences among the steady-state rate constants for the three potentials were of the order of their standard errors, which was about 15% or less. On the other hand, the calculated rate constants exceeded the experimental rate constant by a factor of five to six. Because within the limitations of classical mechanics the calculations were ab initio , it was tentatively concluded that the discrepancy of five to six is due to the use of classical mechanics rather than details of the PES structure.

scholarly journals Control analysis applied to single enzymes: can an isolated enzyme have a unique rate-limiting step?

1993 ◽  
Vol 294 (1) ◽  
pp. 87-94 ◽  
Author(s):  
G C Brown ◽  
C E Cooper
Keyword(s):  
Rate Constants ◽  
General Assumption ◽  
Control Analysis ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Steady State Rate ◽  
Carbamate Kinase ◽  
State Rate ◽  
Rate Limiting ◽  
Control Coefficients

Control analysis is used to analyse and quantify the concept of a rate-limiting step within an enzyme. The extent to which each rate constant within the enzyme limits the steady-state rate of the enzyme and the levels of enzyme intermediate species are quantified as flux and concentration control coefficients. These coefficients are additive and obey summation theorems. The control coefficients of triose phosphate isomerase, carbamate kinase and lactate dehydrogenase are calculated from literature values of the rate constants. It is shown that, contrary to previous assumption, these enzymes do not have a unique rate-limiting step, but rather flux control is shared by several rate constants and varies with substrate, product and effector concentrations, and with the direction of the reaction. Thus the general assumption that an enzyme will have a unique rate-limiting step is unjustified.

Measurement of relative state‐to‐state rate constants for the reaction D+H2(v, j)→HD(v’, j’)+H

1992 ◽  
Vol 97 (10) ◽  
pp. 7323-7341 ◽  
Author(s):  
David E. Adelman ◽  
Neil E. Shafer ◽  
Dahv A. V. Kliner ◽  
Richard N. Zare
Keyword(s):  
Rate Constants ◽  
Relative State ◽  
State Rate

Collisional Deactivation Rates of Electronically Excited Molecular Ions. III.

1972 ◽  
Vol 50 (15) ◽  
pp. 2516-2517
Author(s):  
G. I. Mackay ◽  
J. P. Anglesey ◽  
R. E. March
Keyword(s):  
Electron Beam ◽  
Charge Transfer ◽  
Rate Constants ◽  
Molecular Ions ◽  
Electron Beam Excitation ◽  
Electronically Excited ◽  
State Rate ◽  
Beam Excitation

Electron beam excitation of oxygen was utilized to produce ions in the [Formula: see text] state. Rate constants for the deactivation of [Formula: see text] for each of O2 and N2 were determined. Charge transfer is a possible mode of deactivation.

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