  We have observed an electronic energy level crossing in a molecular
nanomagnet (MNM) using muon-spin relaxation. This effect, not observed
previously despite several muon studies of MNM systems, provides further
evidence that the spin relaxation of the implanted muon is sensistive to the
dynamics of the electronic spin. Our measurements on a broken ring MNM
[H_{2}N^{t}Bu^{is}Pr][Cr_{8}CdF_{9}(O_{2}CC(CH_{3})_{3})_{18}] (hereafter
Cr_{8}Cd), which contains eight Cr ions, show clear evidence for the S=0 to S=1
transition that takes place at B_{c}=2.3 T. The crossing is observed as a
resonance-like dip in the average positron asymmetry and also in the muon-spin
relaxation rate, which shows a sharp increase in magnitude at the transition
and a peak centred within the S=1 regime.
