  The so-called V15 molecule is formed of 15 spins 1/2 antiferromagnetically
coupled. The resultant spin is equal to 1/2. Contrary to what is expected at
first sight, this half-integer spin is gapped. We show that this is a
consequence of the multi-spin character of the molecule. Time reversal symmetry
(Kramers theorem) is preserved due to the existence of a groundstate degeneracy
larger than 2. Magnetization experiments have been performed at different
temperatures, sweeping-field rates and couplings with the cryostat. Their
interpretation in terms of the Landau-Zener-Stuckelberg model gives evidence
for adiabatic LZS spin reversal with and without dissipation.
