  Formation of anomalous isotope abundances in the atmospheres of chemically
peculiar (CP) stars can be explained by light-induced drift (LID). This effect
is additional to the radiative acceleration and appears due to systematic
asymmetry of radiative flux in partly overlapping isotopic spectral line
profiles. LID causes levitation of an isotope with a red-shifted spectral line
and sinking of an isotope with a blue-shifted line, generating thus diffusive
separation of isotopes. We have studied diffusion of mercury as a typical
well-studied isotope-rich heavy metal. Our model computations show that in
mercury-rich quiescent atmospheres of CP stars LID causes levitation of the
heavier mercury isotopes and sinking of the lighter ones. Precise quantitative
modelling of the process of isotope separation demands very high-resolution
computations and the high-precision input data, including data on hyperfine and
isotopic splitting of spectral lines, adequate line profiles and impact
cross-sections. Presence of microturbulence and weak stellar winds can
essentially reduce the effect of radiative-driven diffusion.
