  The low energy spectrum of finite size metallic single-walled carbon
nanotubes SWNTs) is determined. Starting from a tight binding model for the
$p_{z}$ electrons, we derive the low energy Hamiltonian containing all relevant
scattering processes resulting from the Coulomb interaction, including the
short ranged contributions becoming relevant for small diameter tubes. In
combination with the substructure of the underlying honeycomb lattice the short
ranged processes lead to various exchange effects. Using bosonization the
spectrum is determined. We find that the ground state is formed by a spin 1
triplet, if $4n+2$ electrons occupy the SWNT and the branch mismatch is smaller
than the exchange splitting. Additionally, we calculate the excitation spectra
for the different charge states and find the lifting of spin-charge separation
as well as the formation of a quasi-continuum at higher excitation energies.
