  We investigate the influence of convection on the formation of molecular
spectral lines in the atmospheres of late-type giants. For this purpose we use
the 3D hydrodynamical CO5BOLD and classical 1D LHD stellar atmosphere codes and
synthesize a number of fictitious lines belonging to a number of
astrophysically relevant molecules, C2, CH, CN, CO, NH, OH. We find that
differences between the abundances obtained from molecular lines using the 3D
and 1D model atmospheres are generally small at [M/H]=0.0, but they quickly
increase at sub-solar metallicities where for certain molecules they may reach
-2.0 dex. The 3D-1D abundance differences show a significant dependence on the
spectral line parameters, such as wavelength and excitation potential. Our
comparison, therefore, reveals a complex interplay between the spectral line
formation and convection that can not be properly accounted for with the
classical 1D model atmospheres.
