  Intrinsic optical transition energies for isolated and individual single wall
carbon nanotubes grown over trenches are measured using tunable resonant Raman
scattering. Previously measured E22_S optical transitions from nanotubes in
surfactants are blue shifted 70-90 meV with respect to our measurements of
nanotubes in air. This large shift in the exciton energy is attributed to a
larger change of the exciton binding energy than the band-gap renormalization
as the surrounding dielectric constant increases.
