Rationalism in philosphy means more than being rational: it is the belief that you can deduce true knowledge about the world by mere thinking ("apriori synthetic" knowledge).

Imagine you are Einstein, and you have derived relativity from a few axiom, if you are still interested in experimental verification of your theory then you are an empiricist. If you say: I know for sure I'm right no need for experiments at all - you are a rationalist.

Modern science is mostly empiricist, maybe hardcore austrian economists are rationalists (for them economy is derived from praxeology, experimental verification is not possible and not needed)