Triatomic molecules and ions

Translational symmetry. 74 Translawrencium elements, periodicity of. 615-617 Transport, dioxygen, 895-910 Triatomic molecules and ions, molecular orbitals in, 175-182... 

Predict the bond angles at the central atom of the following triatomic molecules and ions (a) ozone, 03 (b) azide ion, N3 (c) cyanate ion, CNO ... 

The electron affinities of several triatomic molecules and the azide radical have been evaluated and are supported by the CURES-EC method. The molecules that are linear in the neutral and bent in the anion have been emphasized. The ECD data support two negative-ion states. Morse potential energy curves for N20 and CS2 have been constmcted for the linear and bent ions. The relative energies of the anion and neutrals for C02, COS, CS2, and N20 were presented to explain the electron attachment data. The electron affinities of the SF molecules n = 1 to 6 were evaluated and the largest values assigned to the ground state. 

In Table 20.1 we compare the valence angles of some representative triatomic molecules or ions formed from elements in Groups 14 to 18. It is seen that the shapes of the molecules are determined by the numbCT of valence electrons carbon dioxide and aU other 16 valence electron species are linear, and species with 17 to 20 valence electrons are angular. When the number of valence electrons is increased to 22, the shape reverts to linearity. The author is not aware of any exception to this trend. 

The simplest intermediate of the nitrogen cation type is the nitronium ion, the active species in most aromatic nitration reactions. There is both cryoscopic and spectroscopic (Raman and infrared) evidence for its existence.802 On the other hand, it has a structure with quaternary rather than electron deficient nitrogen, a structure compatible with the centrosymmetric geometry demanded by the spectra. The Raman line at 1400 cm.-1 has been assigned to the totally symmetric vibration of the linear triatomic molecule. 

The second part of this chapter focuses on actinide chemistry, where we start by describing some triatomic molecules containing a uranium atom, which have been studied both in the gas phase and in rare gas matrices. Most of actinide chemistry occurs, however, in solution, so we then describe actinide ions in solution. The extensive study of the multiple bond between two uranium atoms in the U2 molecule and in other diactinides is then reported. Finally, several examples of inorganic compounds that include U2 as a central unit are presented. 

The application of VSEPR theory to triatomic molecules is exemplified by considering water, carbon dioxide, xenon difluoride and a trio of connected species the nitronium ion, N02+, nitrogen dioxide and the nitrite [or nitrate(III)] ion, N02. ... 

Sr(N3)j is not discussed by Sax (Ref 24) but its effects should be considered similar to those of the alkali and alkaline earth azides Sr azide was first prepd in 1898 by Dennis Benedict (Ref 1) and in the same year by Curtius Rissom (Ref 2) by the action of HNj on the oxide, hydroxide or carbonate of Sr. Its prepn has also been described by Mellor (Ref 7), Gmelin (Ref 9), Audrieth (Ref 10) and others (Refs 11, 15, 18, 19 25). The cryst structure of Sr(N3)2 was investigated to a limited extent by A.C.Gill (cited in Ref 1) and in detail by Llewellyn Whitmore (Ref 15) who established its orthorhmb nature as ionic, with a linear sym azide ion, N N 1.12A, and Sr to N distance of 2.63 to 27lX. Kahovec Kohlrausch (Ref 16) detd, from the Raman Effect, both on cryst powd and in soln, frequencies which corresponded to sym. oscillation in a linear triatomic molecule. 

Included in this section are AH3, AB3, HABa, H2AB molecules, and also dimers, and interactions between diatomics or triatomics and atoms or ions. 

Van der Waals molecules may be classified in various ways, two of which will be mentioned here. For physical purposes in general, and particularly for spectroscopic purposes, the classification introduced by Ewing is valuable. The other possible classification is purely formal and is based on the number of atoms constituting the subsystems of the vdW system under study. Specifically, for example, the first group comprises systems consisting of a rare gas atom (the first subsystem) and a) a rare gas atom, b) another arbitrary atom (or ion), c) a biatomic molecule (or ion), d) a triatomic molecule, e) any other system (a)-e) is the second subsystem). This classification is used in the subsequent text. The former classification makes, e.g., discussion of the vibrational-rotational spectra of vdW molecules more systematic and logical the latter should make, e.g., orientation in an extensive table of vdW characteristics easier and more rapid. 

We have seen, in the case of diatomic molecules, that two-dimensional covariance maps allow correlation of the ion pairs. The situation with regard to the multiple ionization of triatomic molecules is more complex. Similar two-dimensional maps serve to indicate correlations between pairs of ions but at high laser intensities it is probable that three ions will be produced. Although one might infer that three ions have been created simultaneously, the only sure way of confirming the creation and subsequent fragmentation of a triple ion is to use three-dimensional covariance mapping. 

One important aspect of the kinetics is that ion dissociation may not occur during the time between ion activation near the middle of the octopole, and ion detection in the final quadrupole, ca. 30 ps. The efifect of incomplete dissociation on the experimental time scale (the kinetic shift) is negligible for the triatomic atoms and is 0-1 kJ/mol for a larger molecule like the magnitude depending on whether the transition state for... 

There has been much more work on the effect of vibrational excitation on ion reactivity and much of the work up to 1992 has been summarized in two books.Some of this work is outlined below. For diatomic and a few triatomic molecules, it has been possible to detect the vibration state by chemical means, the so-called monitor ion method. 

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