Near-infrared luminescence is observed from single crystals of K 2 PdCl 4 and K 2 PdBr 4 between 13 500 cm -1 and 9000 cm -1 (740 nm and 1100 nm). The emission spectrum of K 2 PdBr 4 shows vibronic structure involving both the totally symmetrical a 1g mode and the non-totally symmetrical b 1g mode (D 4h point group). The luminescence spectrum of K 2 PdCl 4 is less resolved, but shows similar vibronic structure. The maxima of the weak lowest energy absorption bands are at 14 800 cm -1 (molar absorptivity ) 0.42 M -1 cm -1 ) and 14 645 cm -1 (molar absorptivity ) 0.38 M -1 cm -1 ) at 8 K for K 2 PdCl 4 and K 2 PdBr 4 , respectively. The Stokes shifts for K 2 PdCl 4 and K 2 PdBr 4 are 3865 and 3420 cm -1 . A gap of approximately 700 (K 2 PdCl 4 ) or 950 cm -1 (K 2 PdBr 4 ) separates the emission and absorption spectra. This energy gap and the vibronic structure are analyzed with a model involving the E g × b 1g Jahn-Teller effect in the 3 E g excited state of the square-planar [PdCl 4 ] 2and [PdBr 4 ] 2complexes. The Huang-Rhys parameters S a1g and S b1g are 6.7 and 0.2 for K 2 PdCl 4 , leading to bond elongations of 0.12 Å for each of two opposing Pd-Cl bonds and of 0.09 Å for each of the other two bonds. The corresponding values for K 2 PdBr 4 are 7.6 (S a1g ), 0.4 (S b1g ), 0.12 Å, and 0.07 Å.

The templated syntheses of TMA2Sn3S7 and TBA2Sn4S9 (where TMA is tetramethylammonium and TBA is n-tetrabutylammonium) microporous layered tin(rv) sulfides have been carried out under both microgravity (KG) and earth (1G) conditions in order to elucidate the influence of gravity on the self-assembly and crystal-growth processes of this class of materials. The pG experiments were conducted on board the May 1996 Endeavour STS-77 NASA space-shuttle flight. It was determined that the long-range ordering of the porous layers and the population of defects but not the short-range ordering within the layers is influenced by gravity. Bulk and surface crystallinity, smoothness of crystal faces, optical quality, crystal habits, registry of the porous layers, and accessible void volume to adsorbates were found to be improved in the space-grown crystals. This is probably because the forces associated with the organization of the porous layers are expected to be weak and sensitive to the elimination of buoyancy-driven convective flows and Stokes sedimentation effects in a microgravity environment. One can draw an analogy to the weak forces between protein macromolecules and the established effect of microgravity on improving the diffraction quality of crystals harvested in space.

Single-crystal absorption spectroscopy at variable temperature is used to determine exchange couplings between transition metal centers in both the electronic ground and excited states in two new homobimetallic complexes with the formula [LM(y-O)(y-CH3C02)2ML'](C104)2, where M is iron(II1) or manganese(II1).L and L' denote 1,4,7-triazacyclononane and 1,4,7-trimethyl-l,4,7-triazacyclononane, respectively. Values for the ground state exchange coupling constant J are -295 cm-I and +I0 cm-I for the iron and manganese compounds, respectively, using He, = -JS,.S,. Exchange interactions in excited states are qualitatively analyzed, indicating that a spin-forbidden transition of the Fe-Fe binuclear unit occurs with significant intensity by the single-ion mechanism, and not as expected by the Tanabe pair intensity mechanism for spin-forbidden transitions, the dominant mechanism for isoelectronic complexes of manganese(I1).

Spectrochemical determinations of Fe, Mg, Mn, and Ca in garnets by use of a laser micro-probe were performed in matrix. Standards were prepared by fusion of chemically analyzed mineral powders and these standard glasses were excited in the same manner as the mineral unknowns. Comparison of results with the rock standard W-1 showed good accuracy and reproducibility. The precision and accuracy of the method as a whole deems it suitable for most mineralogic investigations where analysis in matrix is desirable.