Optical methods of determining molecular sizes and shapes

5 OPTICAL METHODS OF DETERMINING MOLECULAR SIZES AND SHAPES 

The theory of light scattering is very complicated and the details are beyond the scope of this book the student is referred to books listed at the end of this chapter. The following account will outline the main ideas. 

Schematic diagram of the type of apparatus used in light-scattering experiments. 

The proportion of incident light that is scattered increases with an increase in the number and size of the particles in a solution. If the intensity of the incident radiation is /( , and I is the length of the light path through the scattering solution, the intensity of the transmitted light is given by 

When the particle dimensions are not small compared to X, and the particles are not spherical, the theory is much more complicated. Important contributions to the theory have been made by Gustav Mie in 1908, Peter J. W. Debye (1884-1966) in 1947, Bruno H. Zimm in 1948, and Paul Doty in recent years. By applying their equations to the analysis of the intensity of scattering at various angles it is possible to obtain reliable information about the shapes and sizes of macromolecules. 

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