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The structure of the ionic glasses (KCl) x (BiCl 3 ) 1−x , where x = 0.35, 0.40, 0.45, has been measured at 20 K by using neutron diffraction. The results show that BiCl 3 units exist as the predominant structural motifs at all compositions, give a Bi-Cl nearest-neighbour distance of 2.53(2)Å, and an angle Cl-Bi-Cl of 89(2) • . The nearest-neighbour K-Cl correlations occur at about 3.1Å. The first sharp diffraction peak observed in the total structure factors is attributed to Bi-Bi correlations and the shift in its position to smaller scattering vector values with increased x is attributed to an enlarged separation of the BiCl 3 units with enhanced KCl content. † Now at: Department of Physics, University of Bath, Bath BA2 7AY, UK. ‡ Following Madden and Wilson (1996), we regard an 'ionic' system as one whose properties are reproduced by an interaction model based on discrete closed-shell ions with integer charges, and a 'covalent' system as one whose interactions arise from the formation of chemical bonds involving the sharing of pairs of electrons between atoms. Many properties conventionally attributed to 'covalency' may be explained in terms of 'ionic' interactions provided that effects such as polarization, compression and deformation are taken into explicit account.

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The experimental study of a repetitively pulsed chemical HF laser operating on a chain reaction F 2 +H 2 , initiated by the barrier electrical discharge with the inter-electrode gap 10 cm, with length of active medium 40 cm along optical axis has been carried out. The barrier electrical discharge with duration about 120 ns has shown a high stability, reliability and homogeneity at specific energy deposits up to 60 J / l.At the repetition pulses rate 10 Hz with the depleted fluorine-hydrogen mixture (20 % F 2 , 5 % H 2 ), the mean laser power 500 W (a specific energy for one laser pulse E/V ≈ 11.6 J / l, technical efficiency of 15.6 %) is achieved.In the single pulse mode of the laser operation with the mixture 30 % F 2 , 12 % H 2 the maximum pulse energy E max = 100 J, the specific radiation energy E/V = 24 J / l, the technical efficiency η tech = 28.4 % are obtained.