Optical properties and dust temperatures in clumpy diffuse medium
  In this study, we explore the impact of inhomogeneities in the spatial
distribution of interstellar dust on spatial scales of $\le1$ au caused by ion
shadowing forces on the optical properties of diffuse interstellar medium (ISM)
as well as on the dust temperature. We show that recently proposed possibility
that interstellar dust grains in the diffuse ISM are grouped in spherical
cloudlets (clumps) may significantly affect the observed optical properties of
the diffuse ISM in comparison to that calculated under the commonly accepted
assumption on the uniform dust/gas mixture if the size of clumps $\gtrsim0.1$
au. We found that opacity of an arbitrary region of diffuse ISM quickly
decreases with growth of dusty clumps. We also studied the dependence of
opacity and dust temperature inside the dusty clumps on their size. We show
that the clumps larger than 0.1 au are opaque for far ultraviolet radiation.
Dust temperature exhibit a gradient inside a clump, decreasing from the edge to
the center by several degrees for a clump of a size of 0.1 au and larger. We
argue that dust temperatures and high opacity within clumps larger than 0.1 au
may facilitate somewhat more efficient synthesis of molecules on surfaces of
interstellar grains in the diffuse ISM than it was anticipated previously. On
the other hand, the presence of clumps with sizes below 0.1 au makes small or
negligible influence on the optical properties of the diffuse ISM in comparison
to the case with uniform dust/gas mixture.
