Sp* bond

TABLE VIL6. BARRIERS TO ROTATION AROUND sp- -sp BOND FOR VARIOUS 3-SUBSTITUENTS IN THE A-4-THIAZ0LINE-2-TH10NE SERIES OBTAINED BY DYNAMIC NUCLEAR MAGNETIC RESONANCE. 

Having found a place (the sp -sp bond) to establish the boundary between classical atoms and quantum atoms, the next question is how to cap the quantum atoms. Let s first of all look at an illustrative example of the problem. 

For both forms of graphite the in-plane C-C distanee is 142 pm, i.e., intermediate between Csp Csp and CspMl sp bond lengths, 153 and 132 pm respeetively. Table 1. Consideration of the resonanee struetures between earbon atoms in the plane show that eaeh C-C bond in the earbon layer plane has about one third double bond character. Carbon layer planes (of various dimensions... 

Carbynes are a form of carbon with chains of carbon atoms formed from conjugated C(sp )=C(sp ) bonds (polyynes) ... 

Amorphous carbon films may be broadly classified as (i) amorphous carbon films, a-C films, deposited from carbon-containing gases with low or zero hydrogen content [72] and (ii) hydrogenated carbon films, a-C H films, formed from hydrocarbon-containing gases [73,74]. Both types of film contain different amounts of sp and sp bonded carbon. The amount of sp bonded carbon can be estimated from X-ray absorption near edge spectroscopy,... 

Fig. 23. When lithium inserts in hydrogen-containing carbon, some lithium atoms bind on the hydrogen-terminated edges of hexagonal carbon fragments. This causes a change from sp to sp bonding [37].

Carbon has six electrons around the atomic core as shown in Fig. 2. Among them two electrons are in the K-shell being the closest position from the centre of atom, and the residual four electrons in the L-shell. TTie former is the Is state and the latter are divided into two states, 2s and 2p. The chemical bonding between neighbouring carbon atoms is undertaken by the L-shell electrons. Three types of chemical bonds in carbon are single bond contributed from one 2s electron and three 2p electrons to be cited as sp bonding, double bond as sp and triple bond as sp from the hybridised atomic-orbital model. 

Fig. 4. EEL spectra of (a) graphite and (b) diamond. These carbon allotropes represent different spectra sp bonding especially exhibits 7c -excitation peak lower than the o -excitation peaks (modified from ref. 16).

Carbon with its wide range of sp bond hybridisation appears as the key element of a future nanotechnology. However, so far there is almost no control over the formation processes, and the structures of interest cannot be built at will. Tubes, for example, are produced under the very virulent conditions of a plasma discharge and one would like to have more elegant tools to manipulate the carbon structures, a task which remains a challenge for the future. 

The structure of a-C H DLC consists of an essentially amorphous network with isolated clusters dominated by the sp configuration (graphite) with some sp (diamond). Hydrogen is believed to play an essential role in determining the bonding configuration by helping to form the sp bond, probably in a manner similar to the formation of CVD diamond. 

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