  The electronic spectrum of metallic finite-size single-wall carbon nanotubes
at low energies is derived. It is based on a tight-binding description for the
interacting p_{z} electrons. Not only the forward scattering parts of the
Coulomb interaction, which are diagonalized by bosonization, are considered,
but also all other processes becoming relevant for small diameter tubes. As a
consequence of the substructure of the underlying lattice, a spin 1 triplet is
found as ground state if the exchange splitting is larger than the branch
mismatch, a spin 0 singlet otherwise. Moreover the excitation spectrum is
calculated.
