  Born-Oppenheimer (BO) potential in any material. The proton potential
surfaces in the hydrogen bonded superprotonic conductor Rb3H(SO4)2 are
extracted from the momentum distribution measured using Deep Inelastic Neutron
Scattering(DINS). The potential has a single minimum along the bond direction,
which accounts for the absence of the antiferroelectric transition seen in the
deuterated material, and a saddle point off the bond direction for tunneling
into the next well with a barrier height of 350 meV. The measured potential is
in qualitative agreement with phenomenological double Morse potentials that
have been used to describe hydrogen bonds in other systems.
