Structure general remarks

Sphalerite and wurtzite structures general remarks. Compounds isostructural with the cubic cF8-ZnS sphalerite include AgSe, A1P, AlAs, AlSb, BAs, GaAs, InAs, BeS, BeSe, BeTe, BePo, CdS, CdSe, CdTe, CdPo, HgS, HgSe, HgTe, etc. The sphalerite structure can be described as a derivative structure of the diamond-type structure. Alternatively, we may describe the same structure as a derivative of the cubic close-packed structure (cF4-Cu type) in which a set of tetrahedral holes has been filled-in. This alternative description would be especially convenient when the atomic diameter ratio of the two species is close to 0.225 see the comments reported in 3.7.3.1. In a similar way the closely related hP4-ZnO... 

Different opinions can be found about the status of analytical chemistry as being a branch of chemistry independent from other chemical disciplines or being a physical discipline (Green [ 1992]), or even being an autonomous science, occasionally called Analytics or Analytical Sciences. On the other hand, wide agreement can be stated about the aim to obtain information on matter via representative samples and the inclusion of structural information. Remarks on the general importance of analytical signals can be repeatedly found. 

A few general remarks about homeotect structures. Other important sets of homeotect structure types are those related to disilicide structure types (MoSi2, CrSi2, etc.), cadmium halide structure types, etc. (See Parthe 1964, Hyde and Anderson 1989), or presented by certain groups of compounds such as rare earth trialuminides (Van Vucht and Buschow 1965). 

A few general remarks about a group of metal-hydrogen phases have been included in 3.8.4.1 where interstitial hydrogen solutions in metallic structures have been described. However, as previously observed, a number of intermediate phases are also formed in several systems. A short summary of these is shown in Table 5.2 where their formulae very often have only an indicative character and several structure types correspond to more or less extended solid solution ranges. 

Some more general remarks, however, remain to be added concerning the accuracy of semiempirical calculations and the internal dynamics of the molecule investigated. A closer look at the energy scale of Figure 1 reveals that the minimum for the structure with almost perpendicular CS bonds is a rather shallow one - partly due to the assumed constant geometry for the H CS subunits. The rotational barrier calculated, A 0.04 ev =... 

GENERAL REMARKS ON STRUCTURAL, PHYSICAL, AND CHEMICAL PROPERTIES... 

GENERAL REMARKS ON STRUCTURAL, PHYSICAL, AND CHEMICAL PROPERTIES Table 1.3 Effect of fluorination on boiling points ... 

To what extent does the equilibrium geometry of a molecule change in moving from the gas phase into solution The question is of great importance because, whereas calculations refer strictly to isolated (gas-phase) species, experimental structural data follow from diverse sources gas, liquid, solution and most commonly the solid state. In the absence of proven theoretical models to calculate equilibrium structure in real media, the only way to answer such a question is to compare gas-phase experimental structures with those obtained in solution or in the solid state. This is beyond the scope of the present treatment, and we limit ourselves to a few general remarks ... 

Let us now consider some aspects concerning the relationship between chemical structure and light absorption of organic compounds. We will confine ourselves to a few general remarks. For a more detailed discussion of this topic, we refer to the literature (Silverstein et al., 1991). 

Unfortunately, there are no simple mles to predict reaction quantum yields from chemical structure, and, therefore, Ojr(A) values have to be determined experimentally. We will address such experimental approaches in Section 15.4, and confine ourselves here to a few general remarks. First, we should note that, in principle, reaction quantum yields may exceed unity in cases in which the absorption of a photon by a given compound causes a chain reaction to occur that consumes additional compound... 

Some General Remarks on the Structure of Smectic Polymers 199... 

General Remarks. These equations for the dynamics of a cell mass are in the form of a nonlinear partial integro-differential equation. The nonlocal structure and nonlinearity of the transport term allows for short length scale variation on the order of a cell diamater that models the cellular nature of the aggregate. Equations of a similar form arise in the work of... 

A6.1 General remarks on the band structures of group III nitrides... 

C4.1 General remarks on GaN-based transistors and potential for high temperature/power operation C4.2 GaN FET structures MESFET, MISFET, JFET and MODFET... 

The refinement calculation may be carried out in a variety of ways, and a few general remarks should be made before we consider particular examples. We wish to determine re, /2, /3, and /4, where these denote symbolically the equilibrium structure (which may be thought of as the linear force field), the quadratic, cubic, and quartic force field. (Terms higher than quartic are not considered here.) Each set of data depends on all constants up to a certain order, as shown in Table 3 for example, Ae, Be, and Ce depend only on re, the oo values depend on re and /2, the a values on re, /2, and /3, and the x values on re, /2, /3, and /4. Ideally one should refine all data simultaneously to all force constants (including the equilibrium structure), but in practice the calculation has to be broken down into steps. Thus usually the equilibrium structure re, or some approximation to re, is determined first from the rotational constants then the quadratic force field /2 is determined from the o>, , and r values holding re constrained then the cubic force field /, is determined from the values holding re and /2 constrained and finally the quartic force field /, is determined from the x values holding re, /2, and/3 constrained. (This should be compared with the discussion for diatomic molecules at the end of Section 3.)... 

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