  We study the change in internal rotational energy in the transformation of
protons to neutrons in the \b{eta}-decay reactions that take place in the
collapse of the iron core of massive stars that precede type II supernova
explosions. We consider an ensemble of electrons, protons, neutrons and
neutrinos undergoing \b{eta}-decay reactions, treat the protons and neutrons as
triatomic rotors, evaluate the equilibrium constant to obtain the change in
rotational energy during the proton-to-neutron transformation. We estimate such
change for a variety of conditions, and compare to the energy released in a
supernova explosion.
