  We revisit the theory of the collective neutral excitation mode in the
fractional quantum Hall effect at Landau level filling fractions $\nu=1/3$ and
$\nu=7/3$. We include the effect of finite thickness of the two-dimensional
electron gas and use extensive exact diagonalizations in the torus geometry. In
the lowest Landau level the collective gapped mode i.e. the magnetoroton always
merges in the continuum in the long-wavelength limit. In the second Landau
level the mode is well-defined only for wavevectors smaller than a critical
value and disappears in the continuum beyond this point. Its curvature near
zero momentum is opposite to that of the LLL. It is well separated from the
continuum even at zero momentum and the gap of the continuum of higher-lying
states is twice the collective mode gap at $k=0$. The shape of the dispersion
relation survives a perturbative treatment of Landau level mixing.
