Asymmetric back-bonding

Fig. 5.2-3ir Theoretical surface band structure of Si (100)2 X1, obtained with the asymmetric dimer model (see Sect. 5.2.2.3, Fig. 5.2-7). Ddown and Dup refer to the DB bands at the down and up atoms. The bands labeled Si - S5 and Bi -B5 are back-bond states (modified by the surface) [2.53]...

In a Fischer projection of representing an optically active compound, an asymmetric atom is shown at the intersection point of two lines of a cross. The horizontal lines going to left and right of this point are the bonds extending forward from the plane of paper. The two vertical lines going to top and bottom are those going back away from the plane of paper. For example 2-iodobutane can be represented as ... 

When a molecule absorbs energy in the infrared region (1-300 pm), the a bonds of the molecule begin to vibrate. For simple diatomic molecules, such as H. or HC1, the only possible vibration is a movement of the two atoms away from and back to each other. This mode is referred to as a bond stretch. Triatomic molecules such as CO, have two distinct stretching modes—an asymmetrical and a symmetrical mode. In the symmetrical stretch, both oxygen atoms move away from the carbon atom at the same time. Conversely, in the asymmetrical stretch, one oxygen atom moves toward the carbon atom while the second oxygen atom moves away from the carbon atom. 

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