Ratio Kr Research Articles

Thin‐Layer Cyclic Voltammetric and Scanning Electrochemical Microscopic Study of Antioxidant Activity of Ascorbic Acid at Liquid/Liquid Interface

AbstractAn electron transfer reaction between ascorbic acid (H2A) in an aqueous solution and oxidizing agent in an organic solution immiscible with water has been studied by thin‐layer cyclic voltammetry (TLCV) for charge transfer at the interface between two immiscible electrolyte solutions (ITIES). As an antioxidant, H2A provide electrons through the aqueous/organic interface to reduce Fc+ and the procedure has been proved to be a one electron process again. In this work, the first combination of TLCV and scanning electrochemical microscopy (SECM) was achieved and showed a reasonable agreement between the results from the two different approaches. Otherwise, lower concentration ratios Kr of aqueous to organic reactants was adopted, which is given as evidence to the proposed procedure of Barker.

EFFECTS OF MULTIPLE OBSTRUCTIONS ON CONJUGATE FORCED CONVECTION HEAT TRANSFER IN TUBES

A numerical investigation has been carried out for conjugate forced convection heat transfer in tubes with multiple obstructions. The investigation included the ranges of Reynolds number Re, thermal conductivity ratio kr, and the distance between two obstructions d of 50-600, 0.3-3.0, and 2.0-8.0, respectively. A fluid Prandtl number Pr of 7.56 is used. The obstructions create recirculation flow / back flow in the tube with increase and decrease of local heat transfer rates. Reversal in the direction of heat transfer occurs at certain locations of the tube due to the presence of the obstructions. At high values of Re and d, reversal in the direction of heat transfer occurs on the outer wall after the second obstruction. The overall heat transfer rate decreases with the decrease of kr.

Benzophenone-Sensitized Photolysis of N,N-Dibenzyl-O-acylhydroxylamines. Mechanism of the Imine-Forming Radical Elimination Reaction

Abstract Title hydroxylamines (1) undergo benzophenone-sensitized photolysis to give N-benzylidenebenzylamine (2), p-substituted benzoic acids (3), and monosubstituted benzenes (4) derived from decarboxylation of p-substituted benzoyloxyl radicals. Analysis of the linear Stern–Volmer plots, both for the sensitized photolysis of 1 and for the phosphorescence quenching of benzophenone by 1, demonstrates the participation of triplet 1 in this photolysis. The logarithm of the ratio (kr⁄kd), where kt is the rate constant for homolytic cleavage of the N–O bond in triplet 1 and kd is that for its deactivation, used as a measure of the triplet-state reactivities of 1, exhibited a good Hammett-type relationship against the substituent constant (σ) with a slope (ρ) of −0.75. This indicates the exclusive occurrence of homolysis of the N–O bond in the first excited triplet state of 1. Thus the decomposition of 1 activated by triplet benzophenone is classified as an imine-forming radical elimination. The results of deuterium isotope and micellar effects on the sensitized photolysis suggest that the “out-of-cage” products 4 are obtained by decarboxylation and subsequent hydrogen abstraction of p-substituted benzoyloxyl radicals which escaped from the triplet cage in competition with spin inversion to the singlet cage. In this singlet cage, hydrogen abstraction giving 2 and 3 and recombination affording the starting 1 were found to take place exclusively.

Collision energy dependence of the cross sections for the electronic excitation transfer reactions: Rg(3P0,2)+N2(X 1Σg)→Rg(1S) +N2(C 3Πu) (Rg=Ar, Kr)

The collision energy dependence of the integral cross sections for the title reactions were determined using crossed molecular beams and time-of-flight energy selection techniques. Applying arc-heated rare gas atom beams, the relative collision energies of metastable Ar(3P0,2) and Kr(3P0,2) atoms were selected between 0.4 and 2.5 eV for Ar(3P0,2)+N2, and 0.6 and 1.7 eV for Kr(3P0,2)+N2 systems. The negative energy dependence of the cross sections for the prototype reaction Ar(3P0,2)+N2 agrees well with the results of Parr and Martin in the overlapped energy range (0.4–0.8 eV). The absolute cross sections were determined by normalizing our cross sections to the ones of Parr and Martin. As to the endoergic Kr(3P0,2)+N2 reaction, the product fluorescence from N2(C 3Πu–B 3Πg) was also observed. The total cross section for this reaction exhibits a steep increase near the threshold for each component state [ΔH(3P0)=0.47 and ΔH(3P2)=1.12 eV] and then tends to level off. Assuming the component ratio Kr(3P2)/Kr(3P0) to be statistical in the arc-heated beams, the cross section for each reaction was evaluated by convolution analysis. The post-threshold cross sections for these processes are one to two orders of magnitude smaller than those obtained for Ar(3P0,2)+N2 reaction. The higher reactivity found for Kr(3P2) than for Kr(3P0) is consistent with the quenching rates of Ar(3P0) and Ar(3P2) by N2 obtained by Piper, Velazco, and Setser [J. Chem. Phys. 59, 3323 (1973)]. The present findings suggest that the same type of interaction is also effective for these collision-induced nonadiabatic Kr(3P0,2)+N2 processes as the one, such as spin-orbit interaction, which is applicable between Ar(3P0,2) and N2.

Shock Waves in Chemical Kinetics: Further Studies on the Rate of Dissociation of Molecular Iodine

The rate of the dissociation reaction, M+I2[open phi] lim kRkDM+I+I,has been measured by the shock tube method for argon, helium, nitrogen, oxygen, and carbon dioxide as inert gases, M, in the temperature range 1000°—1600°K. The shock wave results by themselves and the comparison of the shock wave measurements with the room temperature measurements of kR by flash photolysis both show that kR has a negative temperature coefficient. The absolute value of this negative temperature coefficient derived from the shock wave measurements is greater than the value derived from comparison of the average high temperature result with the room temperature result for any particular gas. This may be due to experimental error in the determination of dkR/dT at the high temperatures, but it is believed that the values of kR determined in the middle of the temperature range studied are reliable. The experimental evidence indicates that, for the measurements with CO2, the rate of vibrational equilibration is so fast that the observations made here pertain entirely to vibrationally equilibrated CO2. Evidence from other experiments indicates that the rate of vibrational relaxation in oxygen is such that most of the dissociation reaction occurs in relaxed O2, but that nitrogen remains vibrationally unexcited under the conditions of the dissociation reactions studied here. The ratio, kR, 12/kR,A, of the efficiencies of iodine and argon as third bodies is not greater than 30 at 1300°K whereas it is 250–600 at room temperature. The hypothesis is proposed that in general the ratio kR, gas/kR,A for complex gases will decrease with increasing temperature.