Values Of Reaction Rate Constants Research Articles

A Versatile Trapped Ion Cell for Ion Cyclotron Resonance Spectroscopy

Experimental methods have been developed which permit operation of the standard ICR cell in a trapped ion mode. Appropriate configurations of applied electrostatic fields permit trapping of ions in the source region of the ICR cell. Detection is effected after a suitable delay by drifting the ions from the source through the analyzer region where their power absorption is monitored with the usual marginal oscillator-detector. The minor modifications required do not inhibit normal operation of the cell, thus allowing for the full range of conventional ICR experiments with the additional capability of examining variation of ion abundance with time. The latter mode of operation greatly simplifies elucidation of reaction kinetics. The ion molecule reactions of methyl chloride have been investigated using this new technique. Accepted values of reaction rate constants are reproduced, demonstrating the accuracy of the method.

Reactions Involving Cluster Ions

Rate constants for room‐temperature reactions involving atmospheric cluster ions have been measured using two laboratory facilities: (1) a stationary afterglow facility employing photoionization and separate mass analysis for ions and neutrals, and (2) a drift tube facility employing thermionic emission of alkali ions and mass analysis of ions. In the afterglow facility, the sequence of reactions initiated by NO+ ions reacting in a gaseous mixture of nitric oxide and water vapor and terminated by H3O+·4H2O has been studied at 296°K with each rate constant measured independently. Likewise the sequence of reactions initiated by NO+ ions reacting in a gaseous mixture of nitric oxide and ammonia and terminated by NH4·3NH3 has been studied at 296°K. In the drift tube facility, the clustering of atmospheric gases to the alkali ions Li+, Na+, and K+ has been studied. From laboratory studies of the clustering of atmospheric gases to alkali ions, a map of the minimum values for initial clustering reaction rate constants and equilibrium constants has been drawn. The importance of the formation of a weakly bound cluster ion followed by a switching reaction to form a strongly bound cluster ion to the ion chemistry of the D region has been shown.

Kinetic behavior of antihapten antibody of restricted heterogeneity by stopped flow fluorescence polarization kinetics

Fluorescein, antifluorescein reactions have been studied by initial fluorescence polarization and intensity rate methods. Novel rapid stopped flow instrumentation (msec time range) as well as slower but more sensitive instrumentation has yielded second order rate constants over wide ranges in concentration and time. A bimolecular mechanism for the fluorescein, univalent antifluorescein system has been proposed in which two types of site interactions occur. This mechanism accounts for the fact that fluorescence polarization data consistently yield second order rate constants which are a factor of 10 higher than those obtained from fluorescence quenching data. Comparisons of kinetic behavior of free fluorescein and of fluorescein covalently attached to a normal IgG carrier reacting with Fab antifluorescein have suggested a “carrier effect” of a steric nature. The large equilibrium association constant for fluorescein, antifluorescein systems has been found to be due to extremely small values of the back reaction rate constants; i. e. 10 −3 to 10 −4 as great as those reported for DNP, anti DNP systems.

Similarities between the effect of different flow patterns on diffusion with chemical reaction near an interface

Theoretical models of mass transfer across an interface generally ignore the effect of velocity variation. For mass transfer accompanied by psuedo nth order reaction, it is shown that, at sufficiently high values of reaction rate constant, the rate of mass transfer will be independent of the velocity variation. Thus, in scale-up studies, it is often unnecessary to match flow conditions in laboratory and large-scale equipment, so that laboratory apparatus may safely be chosen on the grounds of simplicity and convenience.

Application of Maximum Likelihood Methods to Ion Swarm Experiments

A new device for performing ion swarm experiments is analyzed mathematically, and expressions for ion swarm distributions in this apparatus are derived. Means are presented for estimating the values of ionic drift velocities, diffusion coefficients (both parallel and perpendicular to the electric field), and ion-molecule reaction rate constants by the use of maximum likelihood estimators. Formulas for estimating the statistical fluctuations of the above estimates which are due to the statistical fluctuations of the ion populations are also presented. Methods for judging the appropriateness of the model used for both the experimental geometry and the ion transport process are discussed. For the purpose of illustrating the techniques, these methods are applied to several data samples for the ions H+ and H3+.

Computer experiments related to chemical propulsion.

I. Introduction T HE use of high-speed computers has played an increasingly important role in the analysis of problems relating to chemical propulsion. In many cases the is merely used for the straightforward evaluation of the analytical expressions resulting from theoretical analysis; however, in an increasing number of problems the has played a central and indispensable role, being used as an apparatus to test theoretical models of the phenomenon under study. The use of such computer experiments'7 to study problems related to chemical propulsion forms the subject of the present survey. It is proposed that a experiment be defined as a theoretical analysis in which the use of the plays the central role in evaluating the consequences of the mathematical model of the physical phenomenon or process being studied. All such experiments involve first a formulation of the problem, second the development of a numerical scheme for solving the equations describing the process in question, then the actual computations, which would generally be impossible without modern high-speed computers, and finally an evaluation and interpretation of the results. The boundary between what can be classed as a experiment and a straightforward calculation will be somewhat arbitrary. Computer experiments take several different forms. In certain cases the physics of the problem is completely understood; however, the mathematical equations describing the phenomenon in question are intractable to analytical solution without the use of severe assumptions. Then high-speed computers are used to numerically evaluate the consequences of the equations. The calculations, made by Fromm 1 and others, of viscous flows over obstacles, and resulting in movies of the computed flow solutions, provide an outstanding example of this type of experiment. In other problems the detailed physics or the value of key physical constants may be uncertain. Thus, for example, reaction rate constant values needed to compute nonequilibrium gas flows may be known only to an accuracy of several orders of magnitude. Such problems are sometimes approached by developing a mathematical model that includes all possible factors of importance. Computer experiments or extensive calculations are then made to establish which factors are important, and which can be ignored. Duff's2 calculations of detonation structure which were carried out for several possible values of the key reaction rate constant provide an early example of this type of experiment.

Lithium Isotope Separation on Complex Formation(II). Kinetic Study of the Exchange Reaction of Lithium Chloride-1, 4-Dioxane Complex

The rate of exchange of lithium isotopes 7Li and 6Li ocurring between lithium chloride and lithium chloride-1, 4-dioxane complex has been studied in 1, 4-dioxane solution at 100°C. The rate constant was calculated from the time dependence of the isotope abundance 7Li/6Li in the complex with the other informations obtained in the preliminary experiments. The apparatus used for the determination of 7Li/6Li is a sector type mass spectrometer with a surface ionization ion source of the triple-filament type. The value of the second order reaction rate constant was found to be(1.99±0.13)×10-2 l·mole-1·sec-1, which is comparable with the rate constants of other similar exchange reactions of metal complexes.

Half-wave potentials for reversible processes with prior kinetic complexity

A kinetic model for electrode processes with prior solution reactions has been explored for the case of reversible electron transfers. A general expression for the current-voltage characteristic has been derived which is valid for all values of the pre-electrochemical solution reaction rate constants. The equations have been applied to the case of polarographic complex ion reductions where either the simple ion, complex ion, or both are electrochemically active. The following results were derived : (1) For very large rate constants, the current—voltage characteristic and half—wave potential are independent of the reaction mechanism. (2) for intermediate and small values of the rate constants, E 1 2 vs. log ligand concentration depends upon the mechanism and is diagnostic for the electroactive species. (3) For complex ion reductions with slow prior solution reactions, the slope of a plot of E 1 2 vs. log ligand concentration yields spurious values of the ligand-to-metal ratio in the complex. (4) A modification of the Lingane—Freyhold—von Stackelberg equation for E 1 2 of reversible complex ion reductions is derived which is valid for all concentrations of the ligand.

EFFECT OF FLUCTUATIONS OF FREE RADICAL CONCENTRATIONS ON THE CALCULATION OF RELATIVE RATE CONSTANTS

The effect of fluctuations in free radical concentrations on the values of relative reaction rate constants calculated from steady state expressions has been evaluated for a number of idealized model cases, representative of various conditions usually encountered in experiments.