  We study collisions in an optically trapped, pure sample of ultracold Cs$_2$
molecules in various internal states. The molecular gas is created by Feshbach
association from a near-degenerate atomic gas, with adjustable temperatures in
the nanokelvin range. We identify several narrow loss resonances, which point
to the coupling to more complex molecular states and may be interpreted as
Feshbach resonances in dimer-dimer interactions. Moreover, in some molecular
states we observe a surprising temperature dependence in collisional loss. This
shows that the situation cannot be understood in terms of the usual simple
threshold behavior for inelastic two-body collisions. We interpret this
observation as further evidence for a more complex molecular structure beyond
the well-understood dimer physics.
