Isotope-dynamic experiment

The basic idea of the isotope-dynamic experiment is as follows. A mixture of a specified chemical composition is fed to the reactor inlet, and changes in the mixture composition are monitored at the reactor outlet. When the composition of the outlet mixture becomes constant (i.e., steady state of the reaction is established), the initial mixture is replaced stepwise with another mixture that has a different isotope composition but is absolutely identical in the chemical composition of reactants. During the isotope substitution, the concentration of isotopes in various substances is measured. 

The procedure of isotope-dynamic experiment provides for the presence of three main components reactor unit, system for the analysis of time variation of the chemical and isotope composition of the reaction mixture, and equipment for switching the initial flows. 

Stability and reactivity of crown-ether complexes, 17, 279 Stereochemistry, static and dynamic, of alkyl and analogous groups, 25, 1 Stereoelectronic control, the principle of least nuclear motion and the theory of, 24, 113 Stereoselection in elementary steps of organic reactions, 6, 185 Steric isotope effects, experiments on the nature of, 10, 1... 

Mason, P.E., Neilson, G.W., Enderby, J.E., Saboungi, M.-L., and Brady, J.W., Structure of aqueous glucose solutions as determined by neutron diffraction with isotopic substitution experiments and molecular dynamics calculations, /. Phys. Chem. B, 109,13104-13111, 2005. 

Second, isotopic substitution experiments using 12CO-13CO mixtures show that the A v = -14 cm-1 shift is the result of two opposing effects, namely, dynamic (Avdyn = 13 cm-1) and static (Avst = -27 cm-1). By standard methods, the dynamic polarizability av was found from the A vdyn value to be av = 0.1007 A. 

Dynamic and static shifts observed for CO adsorbed on a-l e2()2, as determined in isotopic substitution experiments, are similar to those found for CO on MgO Avdyn = 1.5 cm-1 and A vstat = -14 cm-1) (85, 93). This result is also in line with the weak polarization by the strongly shielded Fe3+ ions on (1100) faces av is smaller (0.027 A3) than that of the CO gas (as was found for CO on MgO). The frequency of CO adsorbed on Fe3+ ions can be calculated on the basis of the A vIE relationships discussed previously (528). 

For some systems, there is no resonance Raman or SERS effect to be utilized, and the sensitivity becomes the main problem. In this case, a potential difference method will be of great help [11], Here, a spectrum is acquired at potentials where there is no or only a weak surface signal which is subtracted from that at the potential of interest. In addition, a change in the composition of the electrolyte or an isotopic labeling experiment may be considered to identify the surface species and verify its orientation and structure. For temporally resolved studies, electrochemical transient techniques are helpful to understand the surface dynamics and the reconstruction processes of surfaces. For nonuniform surfaces, spatially resolved measurements provide more reliable and complete information on the surface. This is also useful for electrode surfaces that change either chemically or topographically in a microzone upon variation of potential. 

In fact, molecular dynamics calculations have suggested that the endocyclic pathway may be operative in enzyme-catalyzed processes. In order to delineate the extent to which this alternative pathway occurs in solution, an isotopic scrambling experiment was performed. 

Cochran JK, Buesseler KO, Bacon MP, Livingston HD (1993). Thorium isotopes as indicators of particle dynamics in the upper ocean Results from the JGOFS North Atlantic Bloom Experiment. Deep-Sea... 

Isotopic Tracing with l NO. To trace out the dynamics of nitrogen incorporation into the products under conditions where the surface coverage by adsorbed NO remains constant, experiments... 

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