Low‐Temperature Pair Associates of H Centres in KBr

In the course of investigating the annealing of KBr crystals X‐rayed at 4.2 K the creation of new pair associates of interstitial halogen atoms (di‐H centres) with an absorption band at 3.85 eV is detected. The 3.85 centres arise only as a result of thermodestruction of the well‐known di‐H centres with an absorption band at 4.4 eV. The properties of these new centres are studied and the possible ways of halogen association in KBr are discussed. As a model for the 3.85 centres a model of (Br )2 dimers is proposed, in which the optical transition differs from that in Br ions both by size and direction. The range of KBr absorption spectra between Br and Br absorptions (3.6 to 4.4 eV) is attributed to the absorption of (Br )2 dimers. The V4A centres in KBr with Li or Na impurities have obviously also a (Br−2)2 structure.