The Freely Rotating Polymethylene Chain

The Freely Rotating Polymethylene Chain.—Consider a polymer chain consisting of n bonds of identical length I joined at fixed valence angles 6, The polymethylene chain is a typical example. Vinyl 

There would be left then only product terms for which i=j hence 

The solution of the present problem is made clearer by expanding the summations in Eq. (19) into a square array, thus 

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