How can I find the parameters of a cubic spline data interpolation

Hello everyone,

I am currently working on modelling a complex correlation function . My problem is that this function is hard to modellize. I tried to use a linear combination of 3 exponential and one cosinus functions (with an attenuation of cosinus amplitude). Even with this complex combination, I didn't manage to model properly my correlation function. Thus, I am wondering if, by any chance, there is a way to find the parameters of a cubic spline interpolation (which fits perfectly my complex correlation function)? This could really help me to solve my problem.

Thank you very much for your help!