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By measuring the temperature dependence of the nuclear quadrupole splitting of the Tm 169 8.4-keV Mossbauer y transition, a measure of the strength of the crystalline electric field (CEF) in several hexagonal intermetallic compounds of the type TmX 2 , where X is another transition element, has been obtained. As in thulium metal, a zero-order model of the CEF incorporating only the C2 0 parameter is found sufficient to describe the experimental results. On this basis, the over-all CEF splitting of the Z HQ ground term of the Tm 3+ ion is found to be 94 cm" 1 in TmRu 2 , 88 cm -1 in TmRe 2 , and 42 cm -1 in TmMn 2 . The nuclear and ionic shielding parameters RQ and

By measuring the temperature dependence of the nuclear quadrupole splitting of the 8.42-keV Mossbauer transition in the paramagnetic state of thulium metal, a determination of the crystalline electric field (CEF) parameters of elemental thulium has been obtained. The nuclear quadrupole interaction was studied within the temperature range 59 to 156°K. It was found that a zero-order calculation was sufficient to fit theory to experiment, and that in particular only C 2°, pi, and p 2 ' (where the p's account for shielding constants and the temperature-independent contributions to the electric field graident at the nucleus) were needed to fit the theory to the data, The remaining CEF parameters, C 4°, C 6°, and C 6 6 , were constrained to equal zero in the fitting routine. The over-all splitting of the Z H G ground multiplet was found to be 76.1 cm" 1 . This study also includes a determination of electronic shielding factors for thulium. The atomic Sternheimer factor RQ was found to be 0.16; and the constant

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A Mössbauer temperature study of a cold nematic liquid crystal: Nematic glass-supercooled nematicWe have used the Fe-57 Mossbauer effect (ME) to study solutions (0.2% by weight) of 1,1'diacetylferrocene (DAF) in two liquid crystalline materials, 4-n -butoxybenzylidene-4' on' -octylaniline (BBOA or 40,8) and 4-n -hexoxybenzylidene-4' -n'-propylaniline (HBPA or 60,3). The ME parameters were determined for the temperature range 100--300 K in the crystalline solid phase of both systems and in the cold smectic B phase of BBOA and the cold smectic H phase of HBPA. Here "cold" means the smectic glass and the supercooled smectic phase. The Inf (recoil-free intensity) versus T plots exhibited linear Debye behavior for the solid phases of each system over the entire temperature range. The low temperature portion of the cold smectic Inf versus T data also exhibited Debye behavior for both systems. In both instances the smectic glass gave lower Mossbauer-Debye temperatures (Od than the corresponding crystalline phase. For the smectic H glass of HBPA, 01. = 46 K and is independent of molecular orientation. For the smectic B glass of BBOA, 01. = 64 K for preferred molecular alignment parallel to the ME gamma direction and Of. = 49 K for perpendicular alignment. The smectic glass-supercooled smectic transition was determined to be Tg = 175 K for BBOA and Tg = 190 K for HBPA from the deviation of the Inf versus T data from linear behavior. Above T g , the deviation from linear Debye behavior followed a (T -Tg)2 dependence. For DAF in HBPA, the intermolecular contribution to the Fe-57 vibrational ellipsoid (Ed was isotropic. For DAF in BBOA, EI. declined linearly with increasing temperature below T g • For 220--245 K line broadening and quadrupole relaxation were observed for the supercooled smectic H solution of HBPA. These results are accounted for using a model for rotational diffusion of the DAF molecule. The rotational diffusion apparently occurs without simultaneous translational diffusion.