Cation relaxation

The position of absorption B on the temperature scale depends on the nature and on the number of exchangeable cations. We conclude that absorption B is a cationic relaxation process. The activation energy of absorption B for NaF86.5 agrees with that reported by Matron (10) for their -relaxation process. It is in line with the increase of activation energy for relaxation after adsorption of water on dehydrated Na+-zeolites. Thus, absorption B is caused by the local migration of site III cations over two neighboring sites III, as observed on dehydrated X-type zeolites (8) and on partially hydrated NaX (10). 

An isolated CS plane is referred to as a Wadsley defect and a random array of CS planes is considered to constitute planar (extended) defects which are entirely different from point defects. It is obvious that when CS planes occur at regular intervals, the composition of the crystal is stoichiometric, whereas a random array of CS planes results in nonstoichiometric compositions. While we have invoked anion vacancies which are later annihilated in our description of CS plane formation, we must point out that vacancies are not essential precursors for the formation of CS planes. Accommodating anion-deficient nonstoichiometry through CS mechanism is a special feature restricted to d° metal oxides such as W03, Nb205 and TiOz which exhibit soft phonon modes. Soft phonon modes in metal oxides arise from soft metal-orxygen potentials which permit large cation relaxation. The latter... 

The calculations have been performed to date on Ti407 and TijOg, for which detailed structures are available. To test our proposals relating to cation relaxation the following procedure was adopted. Calculations were performed first on the... 

Thus to summarize, the extent of cation relaxation around a shear plane has emerged from our analysis as the most decisive factor in stabilizing shear planes with respect to point defect structures. Our discussion now continues with an account of the behaviour of the crystals at low deviations from stoicheiometry where an equilibrium may exist between point and extended defect structures. 

LTA, capillary column LTA, catalyst LTA, cation relaxation LTA, crystallisation monitoring LTA, diffusion... 

Relaxations in the double layers between two interacting particles can retard aggregation rates and cause them to be independent of particle size [101-103]. Discrepancies between theoretical predictions and experimental observations of heterocoagulation between polymer latices, silica particles, and ceria particles [104] have promptetl Mati-jevic and co-workers to propose that the charge on these particles may not be uniformly distributed over the surface [105, 106]. Similar behavior has been seen in the heterocoagulation of cationic and anionic polymer latices [107]. 

In such a process, the water molecule fonned in the elimination step is captured primarily fiom the fixmt side, leading to net retention of configuration for the alcohol. For the ester, the extent of retention and inversion is more balanced, although it vari among individual systems. It is clear om die data in Table 5.18 that the two pairs of stereoisomeric amines do not form the same intermediate, even though a simple mechanistic interpretation would sugg that both would fmm the 2-decalyl cation. The coUap of the ions to product is pvidoitly so rapid that diere is not time for relaxation of the initially formed intermediates to reach a common stnicture. 

The fact is that the molecular orbitals describing the resulting cation may well be quite different from those of the parent molecule. We speak of electron relaxation, and so we need to examine the problem of calculating accurate HF wavefunctions for open-shell systems. 

The volumes of activation for some additions of anionic nucleophiles to arenediazonium ions were determined by Isaacs et al. (1987) and are listed in Table 6-1. All but one are negative, although one expects — and knows from various other reactions between cations and anions — that ion combination reactions should have positive volumes of activation by reason of solvent relaxation as charges become neutralized. The authors present various interpretations, one of which seems to be plausible, namely that a C — N—N bond-bending deformation of the diazonium ion occurs before the transition state of the addition is reached (Scheme 6-2). This bondbending is expected to bring about a decrease in resonance interaction in the arenediazonium ion and hence a charge concentration on Np and an increase in solvation. 

Later we will describe both oxidation and reduction processes that are in agreement with the electrochemically stimulated conformational relaxation (ESCR) model presented at the end of the chapter. In a neutral state, most of the conducting polymers are an amorphous cross-linked network (Fig. 3). The linear chains between cross-linking points have strong van der Waals intrachain and interchain interactions, giving a compact solid [Fig. 14(a)]. By oxidation of the neutral chains, electrons are extracted from the chains. At the polymer/solution interface, positive radical cations (polarons) accumulate along the polymeric chains. The same density of counter-ions accumulates on the solution side. 

The smaller cluster ions 83", 84" and 85 + have been examined by Zakrzewski and von Niessen at the HF/6-3H-G level [82]. The lowest cationic states are predicted to be 82, and A" for 83 (Cyv), 84 (I>4h) and (Cs), respectively. The ionisation processes may result in significant structural relaxation leading to the sequence of states different from that of the vertical states. The calculated lowest adiabatic ionisation energies, using the GI method with a very large ANO basis set, are 9.53, 8.05, and 8.20 eV for 83, 84 and 85 , respectively. 

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