Noble gases INDEX

For convenience, the even rarer and less stable krypton compounds are also covered in this entry. All xenon compounds are very strong oxidants and many are also explosively unstable. For a now obsolete review, see [1]. A recent compact review of noble gas chemistry is found in [2], A series of alkali xenates, MH0Xe03.1.5H20 are unstable explosive solids. The equivalent fluoroxenates MFXe03are far more stable. Individually indexed compounds are ... 

Bulk hydrogen and 36Ar contents versus mineral alteration index for CM carbonaceous chondrites. These trends reflect progressive incorporation of water and destruction of the noble gas carrier as alteration advances. After Browning et al. (1996). 

Noble gases are intrinsically difficult to detect by spectroscopy. For example, solar photospheric spectra, which form the basis for solar abundance values of most elements, do not contain lines from noble gases (except for He, but this line cannot be used for abundance determinations). Yet, ultraviolet spectroscopy is the only or the major source of information on noble gas abundances in the atmospheres of Mercury and comets. In the Extreme Ultraviolet (EUV), photon energies exceed bond energies of molecules and the first ionization potential of all elements except F, He, and Ne, so that only these elements are visible in this part of the spectrum (Krasnopolsky et al. 1997). Other techniques can be used to determine the abundance of He where this element is a major constituent. Studies of solar oscillations (helioseismology) allow a precise determination of the He abundance in the solar interior, and the interferometer on the Galileo probe yielded a precise value for the refractive index and hence the He abundance in the upper atmosphere of Jupiter (see respective sections of this chapter). 

In this context the isosteric heat of adsorption approaching zero coverage Qo = Qiso 9 0) is another important quantity. Its experimental determination is more delicate and may be obscured by the fact that the initial adsorption may preferentially occur at surface defects (steps) or impurities due to a stronger binding of the noble gas atoms to these defects. In fact, the increase of Qi at very low coverage observed, e.g., on stepped or high index snrfaces allows to extract the adsorption energy of the defect sites and can even be used as a quantitative measure to determine the defeet concentration. 

It is generally believed then that with metals the electronic configuration, in particular the catalytic activity [21], In this theory it is believed that in the absorption of the gas on the metal surface, electrons are donated by the gas to the d-band of the metal, thus filling the fractional deficiencies or holes in the d-band. Obviously, noble metal surfaces are particularly best for catalytic initiation or ignition, as they do not have the surface oxide layer formation discussed in the previous sections. 

Hale MD, Hileman FD, Mazer T, Shell TL, Noble RW, Brooks JJ (1985), Anal. Chem. 57 640-648.. .Mathematical modeling of temperature programmed capillary gas chromatographic retention indexes for polychlorinated dibenzofurans"... 

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