  It is established within the Thomas -- Fermi model that a bound state of a
proton with a heavy atom should exist. On the one hand, the electrons of the
atom screen the proton's field. This decreases the repulsion force between the
proton and the nucleus. On the other hand, the attraction force between the
proton and the electrons is directed towards the gradient of the electron
density, i. e. towards the nucleus. For instance, for Z=80 both forces become
equal at approximately 0.6a where a is the Bohr radius. The corresponding
minimum of the proton potential energy is in the region of negative energies
(attraction) that can be of the order of several tens of eV. We propose to call
such a system a binuclear atom.
  In contrast to the molecules where a coupling with a hydrogen atom is due to
an essential modification of one or several states of the outer electrons the
formation of a binuclear atom is a result of collective response of the whole
system of inner electrons to the screened potential of a proton that is well
inside the electron system of the heavy atom. The variation of the wave
function of each electron can be considered as a small perturbation. The bound
state is formed as a result of joint action of a large number of perturbed
inner electrons. The important problem concerning the accuracy of our
calculation within the Thomas -- Fermi model is discussed.

Atomic Physics