Noble gases defined

Another very important technique for fundamental consideration of multicomponent systems is low energy ion scattering (LEIS) [Taglauer and Heiland, 1980 Brongersma et al., 2007]. This is a unique tool in surface analysis, since it provides the ability to define the atomic composition of the topmost surface layer under UHV conditions. The signal does not interfere with the subsurface atomic layers, and therefore the results of LEIS analysis represent exclusively the response from the outer surface. In LEIS, a surface is used as a target that scatters a noble gas ion beam (He, Ne, ... 

The method has been confined to main-group compounds presumably because of irregularities expected with unsymmetrical charge distributions in transition metal ions. The noble gas compounds remain outside the scope of the method because of the way in which electronegativity is defined (atom compactness relative to interpolated noble atom compactness). The main weakness of the method when applied to fluorides is in the somewhat arbitrary choice of fluorine bond energies. 

M (a) Elemental abundances and (b) xenon isotopic abundances for some exotic noble gas components (defined in Table 8.2) in meteorites. Modified from Wieler et al. (2006). 

Consider tlie mutual approach of two noble gas atoms. At infinite separation, there is no interaction between them, and this defines die zero of potential energy. The isolated atoms are spherically symmetric, lacking any electric multipole moments. In a classical world (ignoring the chemically irrelevant gravitational interaction) there is no attractive force between them as they approach one another. When tliere are no dissipative forces, the relationship between force F in a given coordinate direction q and potential energy U is... 

Electron clouds do not have sharp boundaries, so we cannot really speak of the radius of an atom. However, when atoms pack together in solids and molecules, their centers are found at definite distances from one another. The atomic radius of an element is defined as half the distance between the nuclei of neighboring atoms (11). If the element is a metal or a noble gas, we use the distance between the centers of neighboring atoms in a solid sample. For instance, because the distance between... 

Partition (Distribution) Coefficients In describing the partitioning of a trace element among coexisting phases, we frequently use a partition (distribution) coefficient for a given element, defined as a concentration ratio C2/Cj. Here C is concentration, and the subscripts identify the phases often the normalizing phase is some convenient reservoir, such as a silicate melt, with which several other phases may equilibrate. For noble gases, it is often most convenient to normalize to a gas phase. If the concentrations are expressed in the same units, the distribution coefficient is dimensionless. It is conventional to cite noble gas concentrations in condensed phases in cm3 STP/g, however, and to describe the gas phase by partial... 

Like solar, the term planetary, as used to describe noble gases, carries a set of connotations well beyond the dictionary definition. Planetary is also used to refer to a pattern of noble gas elemental abundances, and the terms solar and planetary evolved to describe contrasting patterns. The defining feature of planetary noble gases is a much stronger (than in the case of solar gases) elemental fractionation pattern in... 

In summary, we may reasonably conclude that except for Ne, and apart from radio-and nucleogenic components, the isotopic composition of atmospheric noble gases well represent the bulk Earth and can be assumed to approximate a primordial terrestrial noble gas component. Thus defined, primordial terrestrial noble gases are... 

In order to describe the cohesion in the same terms as was done for metals and noble gas crystals, electron density is proposed to accumulate in the vacant interstitial octahedral sites and the remaining tetrahedral sites. This distribution is shown for two CC4 tetrahedral units in Figure 5.17. The central carbon in the outlined tetrahedron is surrounded by an octahedron (in stippled outline) of interstitials defined by the set of vacant tetrahedral sites. 

In the reaction chamber, Ar, a noble gas which does not chemically react with the Fe, is introduced as the reference gas before the introduction of NO. The introduced Ar allows us to define the parameters (see Figure 9.10)... 

In contrast, noble gas paleotemperatures defined in groundwaters from the Carizzo aquifer (Texas) revealed that during the last glacial... 

The poorly defined concept of the metal-metal bond9- sometimes makes it difficult to distinguish between real and false metal-metal bonds. Many metal-metal bonds are only supposed to exist because of intermetallic distances corresponding to those in the metallic state or because magnetic properties or the noble gas rule demand an interaction between neighbouring metal atoms. 

Vibrational spectroscopy is successfully employed to quantitative analysis of gases, especially if real time and on-line analyses are needed. In order to compensate the effects of pressure broadening, it is worthwhile to carry out all measurements at the same total pressure. To this end, the sample is placed in an inert gas, such as nitrogen or a noble gas, and the pressure raised to a defined value. The partial pressure instead of the concentration is used in the Lambert-Beer law. The calibration curve is valid only at the calibration temperature. If the temperature of the sample deviates from this temperature, the partial pressure has to be corrected by the Gay-Lussac law. 

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