In the long-time limit (τ -→ ∞), the internal TCF plateaus at a constant value, known as the generalized order parameter S 2 , which signifies the spatial restriction of the internal motion. S 2 can vary between 1 in the absence of internal motion (fully rigid bond) and 0 for completely unrestricted motion. Numerically, the internal TCF can be approximated by a sum of exponential decays plus an offset,