It is a big surprise and pleasure to have gotten your reply!
I appreciate your answer a lot.
After using the function InterpolatingPolynomial[] I am not sure, though, as to whether or not my goals can be reached in mathematica or at all.
Please have a look at the document and tell me whether it is possible to achieve those goals. The interpolation is not giving me a very good fit on the targeted shape (paro2.nb).
as I understand your problem you just need an interpolation of your 2D data. The idea in this case is to consider the x- and the y-coordinates seperately - see my attachment. Maybe this is helpful.
@Henrik
Thanks very much for your answer!
Is there a way to export the point coordinates and the slope values (first differential) of the various points which I see when doubleclicking on the graph?