Diffraction by molecular helices

摘要

In the present part, we construct the diffraction amplitude of SWNT and MWNT from the form factor of a monoatomic helix obtained in the previous part. This will enable us to simulate numerically and interpret the observed nanotube (NT) electron diffraction (ED) patterns. In order to deepen our understanding of such patterns we perform, with student participation, experiments which simulate the diffraction phenomenon optically. By using specially designed diffraction gratings and a coherent source of light such as a laser pointer, all the essential features of the observed ED patterns can be displayed in the visible range. As a further, related application of great historical interest, the basic helix form factor derived in the first part, along with other suitable optical diffraction gratings, will also be used to interpret the X-ray diffraction picture produced by the celebrated DNA double helix.