Rare gases description

This simple model is adequate for some properties of rare gas fluids. When it is combined with an accurate description of the electrostatic interactions, it can rationalize the structures of a large variety of van der Waals... 

Hope et al. (116) presented a combined volumetric sorption and theoretical study of the sorption of Kr in silicalite. The theoretical calculation was based on a potential model related to that of Sanders et al. (117), which includes electrostatic terms and a simple bond-bending formalism for the portion of the framework (120 atoms) that is allowed to relax during the simulations. In contrast to the potential developed by Sanders et al., these calculations employed hard, unpolarizable oxygen ions. Polarizability was, however, included in the description of the Kr atoms. Intermolecular potential terms accounting for the interaction of Kr atoms with the zeolite oxygen atoms were derived from fitting experimental results characterizing the interatomic potentials of rare gas mixtures. In contrast to the situation for hydrocarbons, there are few direct empirical data to aid parameterization, but the use of Ne-Kr potentials is reasonable, because Ne is isoelectronic with O2-. 

The He2A 2 state has nearly the same dissociation energy as the He (22J ion. This supports the idea that the excited He2 configurations can be described at small interatomic distances as an inner He core with an outer Rydberg orbital. This description is less quantitative for the heavier rare-gas pairs. The unusual maxima result either from curve crossing (e.g., C S ) or as for the state by a changeover in the... 

The techniques described have been used to study the fundamental II2 ion, and its important isotopomers D2 and HD+. Our description of these particular experiments is postponed to chapter 11. Later in this chapter we will describe microwave experiments on the rare gas ions HeAr+, HeKr+ and Ne2, for which rotational transitions, among others, have been studied. 

In the period 1940-1946, Ogg (132) developed the first quantitative theory for the solvated electron states in liquid ammonia. The Ogg description relied primarily on the picture of a particle in a box. A spherical cavity of radius R is assumed around the electron, and the ammonia molecules create an effective spherical potential well with an infinitely high repulsive barrier to the electron. It is this latter feature that does not satisfactorily represent the relatively weakly bound states of the excess electron (9,103). However, the idea of a potential cavity formed the basis of subsequent theoretical treatments. Indeed, as Brodsky and Tsarevsky (9) have recently pointed out, the simple approach used by Ogg for the excess electron in ammonia forms the basis of the modem theory (157) of localized excess-electron states in the nonpolar, rare-gas systems. [The similarities between the current treatments of trapped H atoms and excess electrons in the rare-gas solids has also recently been reviewed by Edwards (59).]... 

It is impossible here to reproduce the results of these numerical methods. Up to now the repulsive forces have been successfully calculated only for the interaction between the rare gas-like ions, not yet for the rare gases themselves. This is not because the repulsive forces between the neutral rare gas molecules constitute a very different problem, but because a considerably smaller degree of exactitude of the repulsive forces gives a useful description, when they are balanced by the strong ionic attractive forces instead of the weak molecular forces only. 

Stoicheff and his collaborators have investigated Brillouin scattering by rare-gas crystals, which is not really an induced process. However, for a quantitative description, significant induced contributions to the polarizability must be taken into account, and it is for that reason that we list relevant work in Section ILL For a review of these efforts and the results obtained see Ref. 139. 

Published theoretical descriptions of the Ca(5 Pi) - Ca(5 Pj) alignment system have considered the formal Landau Zener curve crossing probability [29] and have used foil quantum mechanical descriptions [30]. Unfortunately, all the theoretical descriptions are limited by the lack of accurate potential surfaces for the van der Waals states of the electronic levels. However, in the future, accurate information may become available from recent experiments to investigate metal atom + rare gas van der Waals potentials using supersonic jet spectroscopy [31-34]. Thus there is an excellent chance that it will also be possible to obtain more accurate theoretical descriptions, which will elucidate important subtleties of alignment effects in energy transfer and reactions. 

---