Little is known on the structure and properties of vitreous Se doped with halogens in contrast to group III, IV, V, and VI dopants and also many metal additives. Our Raman measurements of glasses and supercooled liquids in the Se-Cl system indicate the existence of three composition domains: (i) 0 < x < 0.15, where Cl acts as the Se-chain terminator; (ii) 0.15 < x 2) oligomeric units; and (iii) 0.50 < x < 0.70, where the main molecular entities appear to be the Se2Cl2 enantiomers and SeCl4-related molecules. We propose to carry out neutron diffraction measurements of glasses and supercooled liquids in the Se-Cl system in the 3 composition domains in order to complete structural studies of this quite unusual chalcohalide binary system, which exhibits a gradual transition from 1D polymeric to 0D molecular org