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8. Patterson (2)

In this section we will look at the Patterson function of a more complex molecule.
Use to open a second copy of the applet in a new window.

For this exercise there are two copies of the Structure Factor applet - the second is in a new window or tab. This one shows the Patterson resulting from the five marked atoms, and the other shows the electron density itself.

Examine the Patterson carefully, and work out which interatomic vectors correspond to each Patterson peak. There are two peaks (and their opposites) which are higher than the others: one to the right of the origin, and one up and right from that (in fact they are precisely twice as high). Looking at the interatomic vectors, can you work out why?

As the number of atoms increases, the Patterson becomes much more complex and difficult to interpret. Once symmetry is introduced, duplicated vectors become common. Vectors between an atom and one of its symmetry equivalents, known as Harker vectors, can be helpful in trying to interpret the Patterson. These peaks may usually be identified becuase they lie in special sections of the Patterson.