Static reactivity defined

The reactivity most commonly calculated and used is the static reactivity. It is defined as... 

Solving Eq. (3) for the reference critical configuration seldom produces exactly Aq = 1 even though the reactor is known to be critical. This is due to different approximations made in the physical and numerical models, as well as to uncertainties in the nuclear data used for the calculations. For this reason, the static reactivity is often defined, in practice, as = Aq — A. The corresponding perturbation expression is... 

Bonaccorsi ct al. [204 defined for the first time the molecular electrostatic potential (MEP), wdicli is dearly tfie most important and most used property (Figure 2-125c. The clcctro.static potential helps to identify molecular regions that arc significant for the reactivity of compounds. Furthermore, the MEP is decisive for the formation of protein-ligand complexes. Detailed information is given in Ref [205]. 

A vital activity of the chemical sciences is the determination of structure. Detailed molecular structure determinations require identifying the spatial locations of all of the atoms in molecules, that is, the atomic distances and bond angles of a species. It is important to realize that the three-dimensional architecture of molecules very much defines their reactivity and function. However, molecules are dynamic, a feature that is not reflected by static pictures. This last point requires further explanation. Because the atoms in all molecules move, even in the limit of the lowest temperatures obtainable, molecular structures really describe the average position about some equilibrium arrangement. In addition, rotations about certain bonds occur freely at common temperatures. Consequently, some molecules exist in more than one structure (conformation). Some molecules are so floppy that structural characterizations really refer to averages among several structures. Yet other molecules are sufficiently rigid that molecular structures can be quite precisely determined. 

We must note that we are dealing here not with static molecules, as no molecule is stationary even at the absolute zero of temperature, but rather with non-reacting molecules. This will be extended, however, to include mass spectrometry and the reactions which proceed within the mass spectrometry tube, as these are used to define the structure of the parent molecule. Obviously, though, such reactions have an importance of their own which is not neglected. Details of species involved as reactive intermediates, which may exist long enough for definition by physical techniques, will also be considered. For example, the section on ESR (Section 2.04.3.7) necessarily looks at unpaired electron species such as neutral or charged radicals, while that on UV spectroscopy (Section 2.04.3.3) considers the structure of electronically excited heterocyclic molecules. 

The transition state concept, once understood in static terms only, as the saddle point separating reactants and products, may be fruitfully expanded to encompass the transition region, a landscape in several significant dimensions, one providing space for a family of trajectories and for a significant transition state lifetime. The line between a traditional transition structure and a reactive intermediate thus is blurred The latter has an experimentally definable lifetime comparable to or longer than some of its vibrational periods. 

The study of the reactivity of the nucleic acid bases utilizes indices based on the knowledge of the molecular electronic structure. There are two possible approaches to the prediction of the chemical properties of a molecule, the isolated and reacting-molecule models (or static and dynamic ones, respectively). Frequently, at least in the older publications, the chemical reactivity indices for heteroaromatic compounds were calculated in the -electron approximation, but in principle there is no difficulty to define similar quantities in the all-valence or allelectron methods. The subject is a very broad one, and we shall here mention only a new approach to chemical reactivity based on non-empirical calculations, namely the so-called molecular isopotential maps. 

The softness kernels are relevant to the remaining cases of two or more interacting systems. However, they do not by themselves provide sufficient information to constitute a basis for a theory of chemical reactivity. Clearly, the chemical stimulus to one molecule in a bimolecular reaction is provided by the other. That being the case, an eighth issue arises. Both the perturbing system and the responding system have internal dynamics, yet the softness kernel is a static response function. Dynamic reactivities need to be defined. 

The applications of lasers in kinetic studies are essentially twofold. Firstly, they can be used to produce a particular species. This might be a vibration—rotationally defined quantum state of a molecule [21], or it could be an ion [22—24] or fragment [25—28] produced by photoionization or photodissociation [29, 30] of some parent. The combination of specific frequency, short pulse duration and high powers makes selective control of chemical reactions possible. Secondly, they can be used as detectors of specific species and quantum states [31, 32]. There are a number of different methods of using lasers to detect small concentrations of a species in a chemical reaction. Lin and McDonald [33] have broadly reviewed the generation and detection of reactive species in static systems with particular emphasis on the use of lasers for this purpose. 

The synergy of high reactivity and stability in the well-defined isolated reaction environments of nanoscale molecular systems is expected to open undiscovered applications of reactive species to various purposes. Although the covalent frameworks of the molecular cavities described here are very secure and chanically stable, they are static in nature. Interest in stabilization of reactive species by using mechanical bonding systems such as rotaxanes has grown recently. - ... 

Static experiments A bi-layer film of A and B reactive polymers is prepared at a low temperature and is then rapidly heated to a desired reaction temperature to initiate difiiision and interfacial reaction. This type of experiment provides data on an interfacial reaction at a well-defined flat and stagnant interface. Results can then be used for the analysis of the interface while it is simultaneously undergoing deformation. Such an... 

SCC is defined as the growth of cracks due to the simultaneous action of a stress (nominally static and tensile) and a reactive environment. For metals, "reactive" excludes gaseous hydrogen, cathodic polarization, and liquid metals but includes aqueous and nonaque-ous electrolytes and reactive atmospheres (H2O, I2, CI2). Related phenomena occur in inorganic glasses and ceramics, especially in water, and are thought to be involved in major... 

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