Ionization rate constant

Fig. 2. A plot of log ionization rate constant against log acid dissociation constant for some carbon acids in water at 25°, 346...

Table II. Calculated Ionization Rate Constants for Diphenylmethane in Dimethyl Sulfoxide (80% )— f erf-Butyl Alcohol Solutions...

The catalyst in the absence of fluorene absorbed oxygen, and in Table V a correction for this process has been attempted. The corrected data indicate an ionization rate constant of fluorene of 1.2 0.2 mole"1 per second at 29.5°C. The isotope effect in ionization of fluorene and 9,9-dideuteriofluorene is thus about 10. 

Final confirmation of this interpretation was attempted by studying the electron transfer between fluorene and m-trifluoromethylnitrobenzene in basic solution monitored by ESR spectroscopy in the absence of oxygen. Table VI summarizes data yielding an ionization rate constant of 0.9... 

These latter measurements led only to relative cross-section values. However, by comparison with absolute values of velocity-averaged cross sections, they can be put on an absolute scale. To do this, the absolute values obtained in FA measurements were used because here the velocity distribution is exactly known—a Maxwellian distribution /(t>, T) with the temperature of the buffer gas. Denoting the velocity-dependent relative total ionization cross section, obtained in the beam experiment, by oKl(v) and the absolute total ionization rate constant obtained in the FA experiment by R(T), then a normalization k may be determined by... 

Fig. 11.15 Principal quantum number dependence of the experimental rate constants for the total depopulation of the Xe nf states by NH3 ( ) and for collisional ionization (O). Also shown is the calculated ionization rate constants of Rundel (R) (ref. 69), Latimer (L) (ref. 10), and Matsuzawa (M) (ref. 70) (from ref. 64).

A very interesting paper80 reported studies of the reactions of several substituted benzhydryl carbenium ions, generated by laser flash photolysis, with halide ions in several solvents. This work provided the nucleophilicity N of chloride and bromide ions in several solvents. These data, along with the ionization rate constants and the solvolysis rate constants for the reactions of substituted benzyhdryl halides, was used to construct quantitative energy surfaces for the. S N 1 reactions of substituted benzhydryl halides in several solvents. 

Here an important definition for the rate constant of free carrier production, k, is given. The latter differs from the ionization rate constant by a multiplier equal to the charge separation quantum yield tpm, obtained in the Markovian approximation. This difference indicates that the number of photogenerated ions that avoid geminate recombination and become free is less than their total amount, cpm < 1. 

Possible applications of laser enhanced ionization in flame diagnostics are 1. simultaneous observation of ionization and fluorescence signals from various levels might provide more information on the sequence of processes leading to and from the ionization continuum 2. the measurement of ion mobilities, relating to cross-sections for elastic collisions between ions and flame particles 3. measurement of ionization rate constants relating to cross-sections for inelastic collisions between excited atoms and other flame particles 4. measurement of recombination rate constants, relating to cross-sections for inelastic collisions between ions, electrons and neutrals. 

Winstein (1957c). They argued that during solvolysis of neophyl substrates [46, X = Cl, Br] internal return from the proposed phenonium ion-pair intermediate [47] would yield the tertiary derivative [48] (Fig. 13) and this would solvolyse rapidly. Thus, the titrimetric rate constants should correspond to the ionization rate constant k j (Fig. 2). Later neophyl tosylate [46, X = OTs] and its p-methoxy derivative were used (Smith et al., 1961 Diaz et al., 1968b Yamataka et al., 1973), and recently Schadt et al. (1976) defined as a scale of solvent ionizing power for tosylates, designated F2-AdOTs or Yqt, using eqn (5) but based on 2-adamantyl tosylate [6] instead of t-butyl chloride. A correlation of the rates of solvolysis of neophyl tosylate with F0 Xs (Fig. 14) is satisfactory (correlation coefficient... 

The ionization rate constants (fcj) for the 5 1 reactions of various diarylmethyl chlorides whose Ef values are known have been measured in the presence of piperidine, pyridine, or PPhj, which suppresses ion-pair return, in several dipolar aprotic solvents. The Hammett p values range from -4.0 to -4.3 in the different dipolar aprotic solvents, proving that the reactions occur by an 5 1 mechanism. The nucleofu-gality parameters Nf and Sf from the log k = Sf Ef + Nf) equation) for the diarylmethyl... 

The question about the relation between the reactivity of reactants and their structure is one of the fundamental problems of chemistry. This problem as one of the main directions of chemical kinetics was formulated in the general form about 100 years ago by N.A. Menshutkin in his works on hydrolysis of esters. One of the most important directions in this area is correlation equations relating the reaction rate constant to thermodynamic and structural parameters of reactants. The first correlation was proposed by Ch. Taylor (1914) who noticed a proportionality between the ionization rate constant of the catalyst and rate constant of the catalyzed reaction. The systematic work on correlations in chemical kinetics started from the works of J. BrSnsted and K. Pedersen who, using the results of their study of the reactions catalyzed by acids ( ha) and bases ( a), proposed the equations relating the rate constants of catalytic reactions to the dissociation constants of acids ituA (1924)... 

Ionization rate constants in aqueous acetonitrile were obtained for trityl chlorides, bromides, and acetates covering 21 units in the pA1r+ of the trityl cation. This study observed solvolyses with and without common ion return, solvolyses where the trityl cation could be observed to form and then decay, solvolyses where water addition occurs before complete formation of the cation, and at the other extreme, solvolyses that yield persistent carbocations. Mayr and coworkers showed how electrophilicity and nucleophilicity parameters rationalize reactivity patterns and resolve mechanistic controversies in organocatalytic cyclizations. The thermodynamic affinities of a large number of Lewis bases were computed for addition to the methyl, diphenylmethyl, and triphenyl-methyl cations. ... 

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