TY - JOUR A1 - Ahlert, D. A1 - Franz, Robert U. A1 - Hohlwein, D. A1 - Prandl, W. A1 - Schiebel, P. A1 - Siemensmeyer, K. T1 - Die partielle Konversion von inkohärenter in kohärente Streuung an Protonen : das Ausfrieren der Quanten-Spin-Fluktuationen beim freien NH3-Rotator in Ni(NH3)6(PF6)2 JF - In: Zeitschrift für Kristallographie / Supplement issue No. 9 (1995) , p. 82 Y1 - 1995 SP - 82 ER - TY - JOUR A1 - Schiebel, P. A1 - Ahlert, D. A1 - Franz, Robert U. A1 - Hohlwein, D. A1 - Prandl, W. A1 - Siemensmeyer, K. A1 - Wulf, K. T1 - Partial conversion of neutron incoherent into coherent scattering by NH3 quantum rotators JF - In: Physica B: Condensed Matter 226 (1996) 1–3, pp 234–237 N2 - Neutron diffraction experiments on powders are used to investigate the quantum mechanical behaviour of uniaxial rotators, i.e. NH3-molecules in Ni(NH3)6(PF6)2, Co(NH3)6(PF6)2 and Ni(NH3)6I2. A diffuse temperature dependent component of the total scattering, modulated ∼ sin QrH-H/QrH-H, is observed at a temperature of ≃ 20 K and below. This observation is due to the fact, that on cooling the sample to kT ∼ B (rotational constant) the rotational ground state is strongly populated. The ground state of a uniaxial free rotator, however, is completely polarized. As a consequence the scattering of those NH3 groups being in the ground state becomes coherent and is observable in diffraction experiments. Y1 - 1996 U6 - https://doi.org/10.1016/0921-4526(96)00312-2 SP - 234 EP - 237 ER -