Bond angular distributions

Fig. 14.9 O-B-0 and B-O-B bond angular distributions obtained at 300 K for the boroxol-poor (/ = 22%) and boroxol-rich (/ = 75 %) models...

Unpronounced polarization of regular C-H bonds such as methyl or ethyl groups does not lead us to expect the formation of dihydrogen bonds. Actually, an analysis of the Cambridge Structure Database [2] reveals numerous C-H- - -H-C contacts with H- - -H distances of 2.500 A or even more where the angular distribution is ideally isotropic. The latter is typical of nondirec-tional van der Waals interactions. The C-H and B-H bonds in the molecule l,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene- BH3 are obviously more... 

Photon-induced emission of electrons is an obvious tool for structural analysis in two ways. Firstly, it is sensitive to the initial density of states of the emitted electrons (originating from the first few atomic layers of a surface), and so to the surface geometry. Secondly, if the angular distribution of the emitted electrons is considered, additional information about the initial electron states (in particular orbital shape and bonding... 

The different stable orbitals of an atom which can be used for bond formation do not differ very much from one another in their dependence on r, but they may show a great difference in their angular distribution. This can be seen from Figure 4-1, representing the angular distribution of an orbital and the three p orbitals.2 The s orbital is spherically symmetrical, and hence can form a bond in one direction as well as in... 

The results presented here show that the energy distributions of the parent molecular species, e.g. benzene, are narrower than those of atomic species, even though the ejection processes in both cases arise from energetic nuclear collisions. The bonding geometry also Influences the ejection yield and angular distribution. The specific case of it-bonded and o-bonded pyridine on a metal surface is discussed with comparisons between the calculated results and experimental data. 

The arrangement of the molecules on the surface also Influences the angular distributions of the ejected species (22). The polar angle distributions of various ejected ions for four systems -2.5 L benzene (monolayer), 4.5 L pyridine (monolayer, o-bonded) 0.15 L pyridine (ir-bonded), and 12 L thiophene (monolayer) on Ag(lll) have been measured. The results of these distribution measurements are illustrated in Figure 3. For... 

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