Dipole-dipole attractions are a type of intermolecular forces of attraction found in molecules having a permanent dipole like SO2, NH3 etc. Halogen molecules are homonuclear diatomics, bound by a shared covalent bond between two atoms. The atoms at the two sides of the bond are identical, and as a result the shared electron pair resides exactly at the centre of the bond joining the two. That means, there is no development of permanent polarity within the molecule. In other words the halogen molecules are non polar. So there is no question of a dipole – dipole intermolecular force of attraction in halogen molecules. Temporary dipoles, however, are induced and such induced dipole – induced dipole interactions bind different molecules of halogens together.