The heavier noble gases

Ne in MORE has °Ne/ Ne and Ne/ Ne ratios that are significantly higher than those of the atmosphere (9.8 and 0.029, respectively) and fall on a correlation line that is widely interpreted as due to mixing between atmospheric contamination and an upper mantle component. This component in turn is a mixture of solar Ne with a high e/ Ne ratio and radiogenic Ne. Samples from high He/ He OIE have similar 

This has been interpreted as an indication that such an OIE domain has contributed noble gases to the continental lithosphere, and will be discussed further in the section on the Victorian Newer Volcanics. Matsumoto et al. (1998) found measured He/ Ne ratios that were equal to, or lower than, the values for the convecting mantle, suggesting that recent loss of He occurred in some cases. Such losses could occur from the host mineral or from a fluid that introduced the rare gases into the xenolith, e.g., a fluid that has previously lost some CO2 in which He preferentially entered relative to Ne. 

A range of values has been measured in MORB. The highest 

Ichinomegata, Japan that appear to sample the mantle wedge above a subducting slab. 

Nagao and Takahashi (1993) reported values from total fusion measurements of °Ar/ Ar 1900, and suggested that this was due to subduction of atmospheric Ar. While evidence for the subduction of Ar into the mantle, and possibly into the continental lithosphere, would be important for understanding mantle Ar evolution (see Porcelli and Ballentine 2002, this volume), the alternative that these samples have been contaminated by posteruption contamination in the same way as samples from other localities have been cannot be discounted. 

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Neon is a monatomic atom that is considered relatively inert. It does not even combine with itself to form a diatomic molecule, as do some other gases (e.g., and O ). During the 1960s it was discovered that the noble gases are not really inert. Neon and the heavier noble gases (Kr, Xe, and Rn) can form compounds when in an ionized state with some other elements. For example, neon can form a two-atom ionized molecule of NeH. Neon has also been forced to form a compound with fluorine. 

For the heavier noble gases, the core multiplicity of the metastable states give rise to eight potential curves (six for 3P2 and two for 2P0). The Ne2 potentials have been calculated by Schneider and Cohen,87 who have also performed scattering calculations for this system. Theoretical and experimental data exist for Ar2,88 whereas only qualitative estimates of the potentials are available for Kr2 and Xe2. These excited states play a prominent role in the rare-gas excimer lasers.89,90 ... 

Table 6.9 Covalent bonding of the heavier noble gases...

Double-ionization studies of the heavier noble gases have also been reported by Charlton et al. (1989), Kruse et al. (1991), Helms et al. (1994a, 1994b, 1995) and Kara et al. (1997a). Although there are small differences... 

Triple ionization of the heavier noble gases has been reported by Kruse et al. (1991) and Helms et al. (1994, 1995a), and again the influence of inner shell effects is notable and quickly becomes the dominant mechanism for this process. 

In this section we describe experiments whose aim has been to determine explicitly inner shell ionization cross sections (or ratios of electron and positron cross sections). Section 5.5 contained an account of the influence of inner shell processes on multiple ionization of the heavier noble gases. 

Sorption of the heavier noble gases on ice might be interesting (cf. Section 7.5), but there are no relevant data. 

Figure 6.5 Correlation plots between 36 Ar abundance and 3He, 20Ne, 84Kr, and 132Xe abundances (cf. Table 6.1 for data source). Note that even though there are good correlations among the heavier noble gases (Ne in OIB Ar, Kr, and Xe in MORB and OIB), correlations between He and the heavier noble gases are totally lacking.

These observations suggest that the heavier noble gases, Ne (except for in MORB), Ar, Kr, and Xe had behaved concomitantly throughout the whole geological processes until they were finally trapped in the glassy margins of the OIB and MORB samples. 

On the other hand, He and Ne in MORB behave quite differently from the heavier noble gases. As seen in Figure 6.5, there is no correlation between He-content (and... 

Noble gases are nearly chemically inert. The heavier noble gases form a number of compounds with oxygen and fluorine such as KrF2 and Xe04... 

These deviations are still appreciable for the more realistic Me3Si noble gas complexes (Fig. 11). It is not likely that "free" silyl cations will be present in matrix isolation, in argon and the heavier noble gases. 

In 1933, besides some theoretical speculations that noble gas compounds should exist, some new reports of unsuccessful experiments to prepare noble gas compounds were published. The most promising experiment was carried out by Yost and Kaye at the suggestion of Pauling, who was convinced that at least the heavier noble gases, for example, xenon, should react with the most electronegative elements, for example. 

There are few constraints on the heavier noble gases in ultramafic xenoliths. While obtaining credible heavy isotope compositions is hampered by low concentrations, more refined analyses and... 

Martian mantle noble gases. Martian meteorites contain components other than those derived directly from the atmosphere (see detailed discussion by Swindle (2002)). Information on the relative abundances of the heavier noble gases in the mantle (Ott, 1988 Mathew and Marti, 2001) suggests that the " Kr/ Xe ratio is at least 10 times lower than both the martian atmosphere and the solar composition. If this is truly a source feature, it indicates that heavy noble gases trapped within the planet suffered substantially different elemental fractionation than the atmosphere (see Chapter 4.12) and have not subsequently formed a dominant fraction of the atmosphere. However, it is not possible at present to conclusively determine whether the measured elemental abundance ratios reflect an interior reservoir that was initially different from atmospheric noble gases, rather than due either to planetary processing or transport and incorporation into the samples. 

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