  We have studied the bound states of the extra electron in a molecular wire,
corresponding to the physical situation of the electron tunneling through the
wire. Based on formalism of the scattering operator that accounts for
many-electron interactions we have shown that the energy spectrum of the bound
states of the extra electron in a linear chain of three-dimensional scattering
centers substantially deviates for spectrum of independent single-electron
states of Bloch electrons in a system described by a single-electron effective
potential. In particular, in the case of elemental wire consisting of the
centers with one electronic state per center, the number of states in the band
can be less than number of centers of the wire. These states form two bands
instead of single band and the bands exhibit non-analytical, square root
dispersion in the vicinity of the point where both bands come together. These
findings are important for developing physically viable theory of electron
tunneling in single molecular systems because the structure of spectrum of
electron's bound states and its relative position in respect to the Fermi
levels of electrodes determine specific mechanisms of electron transport
through a molecular wire.
