  Below 360 mK, Fe8 magnetic molecular clusters are in the pure quantum
relaxation regime. We showed recently that the predicted ``square-root time''
relaxation is obeyed, allowing us to develop a new method for watching the
evolution of the distribution of molecular spin states in the sample. We
measured the distribution P(H) of molecules which are in resonance at the
applied field H. Tunnelling initially causes rapid transitions of molecules,
thereby ``digging a hole'' in P(H). For small initial magnetisation values, the
hole width shows an intrinsic broadening which may be due to nuclear spins. We
present here hole digging measurements in the thermal activated regime which
may allow to study the effect of spin-phonon coupling.
