  In this paper we present the results on Raman-active modes calculation in
achiral $(n,n)$ and $(n,0)$ carbon nanotubes (CNTs). vibrational spectra are
derived as the eigenvalues of corresponding dynamical matrix at the
$\Gamma$-point of Brillouin zone. Diagonal components and $\alpha_{xy}
(=\alpha_{yx})$ are the only non-zero components of polarization tensor.
Selection rules for Raman-active modes are determined by direct estimations of
matrix elements responsible for the intensities of corresponding vibrational
transitions. Few $E_{2g}$ modes can be non-Raman-active because of their
``fine'' vibrational structure. We claim that numbers of Raman-active modes for
achiral CNTs are: 5 ($(n,n)$ and $(n,0)$, $n$-even); 6 ($(n,n)$, $n$-odd); 8
($(n,0)$, $n$-odd).
