Local bonding configuration

On the basis of the observations mentioned above, we conclude that the vibration at 1875 cm-1 is a Si—H vibration. This follow from (1) the sharpness of the feature, linewidth less than 50 cm-1, and (2) the frequency relative to the range of measured B—H and Si—H frequencies. Figure 15 presents a model for the local bonding configuration involving the H atom. This model accounts for the frequency of vibration as well... 

The interpretation of the broad line is somewhat more ambiguous than the interpretation of the narrow line. Because the broad line occurs in films with dihydride or trihydride sites as well as in films with only monohydride sites, there is no direct correlation between the sites that constitute the broad line and the local bonding configurations indicated by the infirared absorption measurements. Evidently many kinds of clustered environments can contribute to the broad line. The most commonly accepted interpretation of this line is that it is due to the hydrogen atoms bonded on the internal surfaces of small voids (Reimer et ai, 1981b Jeffrey et ai, 1981a Carlos and Taylor, 1982b). 

A Useful Comparison. There are striking similarities in the local bonding configuration of some surface sites and some dissolved complexes. Compare, for... 

The delocalization of excessive a- (or P-) spins and the bond polarization can take place among radical orbitals, p and q, and the central n (or o) and n (or o ) orbitals, resulting in the electron transferred configurations (T) and locally excited configurations (E), respectively (Fig. 5a). The delocalization-polarization mechanisms are different between singlet and triplet states, as addressed in the following subsections. 

Inelastic shearing of atoms relative to one another is the mechanism that determines hardness. The shearing is localized at dislocation lines and at kinks along these lines. The kinks are very sharp in covalent crystals where they encompass only individual chemical bonds. On the other hand, in metal crystals they are often very extended. In metallic glasses they are localized in configurations that have a variety of shapes. In ionic crystals the kinks are localized in order to minimize the electrostatic energy. 

The vibrational motion of polyatomic molecules encompasses all nuclei in the molecule and, as long as the displacement from the equilibrium configuration is sufficiently small, it can be broken down into the so-called normal-mode vibrations (see Appendix E). In special cases these vibrations take a particular simple form. Consider, e.g., a partially deuterated water molecule HOD. In this molecule, the H OD and HO-D stretching motions are largely independent and the normal modes are, essentially, equivalent to the local bond-stretching modes. To that end, consider the following reaction that has been studied experimentally [6,7] as well as theoretically [8] ... 

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