71701720.8413 Megatons to stop rotation, considering the largest explosion ever was about 50MT, we'd need 1.5 million of those.
assume the moon is solid, workout the moment of inertia and kinetic energy.
Sound reasonable.
Side note: It is true what nsimmons state, that the largest human made explosion ever was about 50MT, the Tsar Bomba. However it is a 3-stage hydrogen bomb, 100MT, but was scaled down to 50% for the test explosion.
You ever see the newer time machine movie? Where in the future they used nukes to excavated on the moon and split it in half. This is what i think would happen.