  We show that interstitial hydrogen nucleii on a metallic lattice are strongly
coupled to their near neighbours by the unscreened electromagnetic field
mediating transitions between low-lying states. We then show that in
almost-stoichiometric PdD clusters, in which most interstitial sites are
occupied by a deuteron, certain specific superpositions of many-site product
states exist that are lower in energy than the single-site ground state,
suggesting the existence of a new low temperature phase. The modified behaviour
of the two-particle wavefunction at small separations is investigated and
prelimary results suggesting an over-canceling of the effective Coulomb barrier
are presented.
