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The indides RE 12 Fe 2 In 3 (RE ϭ Ho, Er, Tm, Lu) have been prepared by arc-melting the elements and subsequent annealing. All compounds were characterized by X-ray powder diffraction and the Er 12 Fe 2 In 3 structure was refined from X-ray single crystal data: I4/mmm, a ϭ 958.8(1), c ϭ 957.8(1) pm, wR2 ϭ 0.0629, 412 F 2 values and 22 variables. The 2a site shows In/Fe mixing, leading to the composition Er 12 Fe 2.31 In 2.69 for the investigated crystal. The structure (new type) derives from a Cu

Degradation of gas mixtures and methods of its reduction in lasers were studied with reference to the DC-excited, transverse-flow CW laser of MLT 1200 type. The long-term output characteristics and their dependence on the mixture's composition determined in the experiment gave a hint concerning the thorough theoretical analysis of decomposition in laser mixtures. The observed optimal concentration of lies within the range and that of is about 2 - 3% for the laser under consideration. In the theoretical analyses of available data we focus our attention on the roles played by the gas pressure, the mixture composition and the growth of the afterglow region in the reduction of working gas degradation. The equilibrium conversion decreases with increasing gas pressure. A 50% reduction in is obtained when the pressure increases from 13.33 to 46.66 hPa. The observed optimal composition corresponds to low reactivity of the laser plasma with a small oxygen content. The optimal period for the laser gas mixture to reside in the afterglow region is larger by a factor of 1000 than the discharge residence time. The relatively small value of the equilibrium conversion in the MLT 1200 laser results from relatively high concentrations of atomic and electronically excited species. The formation of atomic oxygen is inhibited by reactions with electronically excited molecules, especially . Only very small concentrations of and , which are the most harmful reaction products, result according to our calculations for the MLT 1200 system.