The concept of dynamic trajectories on the potential energy surface of magnetic and exchange interactions for cage reactions in a radical pair is formulated. The magnetic effects induced by static as well as by a combination of static and radiowave magnetic fields are considered as tools for magnetic probing of the exchange potential along the dissociating bond. Transition state radio-spectroscopy as an analogue to the transition state femtosecond spectroscopy, developed by Zewail, is suggested.