  We have assigned the chirality of the internal tubes of double walled carbon
nanotubes grown by catalytic chemical vapor deposition using the high
sensitivity of the radial breathing mode (RB) in inelastic light scattering
experiments. The deduced chirality corresponds to several semiconducting and
only two metallic internal tubes. The RB modes are systematically shifted to
higher energies when compared to theoretical values. The difference between
experimental and theoretical energies of the RB modes of metallic tubes and
semiconducting tubes are discussed interms of the reduced interlayer distance
between the internal and the external tube and electronic resonance effects. We
find several pairs of RB modes corresponding to different diameters of internal
and external tubes.
