2.3 Hindered Rotation Chain

  ⟨R2⟩  =  C  nl2
           (∞       ) (         )
   C∞   =    1+-cosθ-  1-+-⟨cosφ⟩
             1- cosθ   1 - ⟨cosφ⟩
           ∫2π cosφ exp(- U (φ )∕kT )dφ
⟨cosφ⟩  =  -0∫-2π-------------------                        (10)
              0  exp(- U(φ)∕kT )dφ