Reorientational motion of the HS− ions in hydrogensulfides of alkali metals (NaHS, KHS, RbHS): A quasielastic neutron scattering study

Abstract

The isostructural hydrogensulfides of the alkali metals sodium, potassium, and rubidium were investigated by quasielastic neutron scattering in order to gain insight into the dynamics of the molecular anion HS− as a function of temperature. A phase transition between the rhombohedral middle temperature modification (MTM) and the cubic high temperature modification (HTM) of the title compounds was of special interest. A two site jump model is clearly supported by the data of the MTM and an eight site jump model is consistent with the data of the HTM. The jump distances are in reasonable agreement with distances of the hydrogen positions determined by neutron powder diffraction on the fully deuterated samples. At the MTM→HTM phase transition the correlation times of the reorientational motion decrease by about one order of magnitude. Within the investigated temperature range (T=170 K to T=450 K) they change from 10−8 s to 10−12 s. They show Arrhenius behavior. The activation enthalpies of the MTM decrease with increasing radius of the cation from 26(1) kJ mol−1, 22(1) kJ mol−1 to 18(2) kJ mol−1 for NaHS, KHS and RbHS respectively. In the HTM they are equal within the estimated error 6(1) kJ mol−1 and 7(1) kJ mol−1 for NaHS and KHS.

Dynamics of anions and cations in cesium hydrogensulfide (CsHS, CsDS): Neutron and x-ray diffraction, calorimetry and proton NMR investigations

“…A high mobility of the ions in the HTM can also be expected from the enhancement of crystal quality at high temperatures. 8 A similar behavior of T 1 was observed for M HS with M ϭNa, K, Rb 18,20 and an increase of activation energies with an increasing radius of M favor a diffusion of the cations. Nevertheless, the activation energies are quite low for long-range translational motion in solids.…”

“…[1][2][3][4][5] The dynamics of the anions were analyzed by the use of IR/Raman spectroscopy, [6][7][8][9] inelastic and quasielastic neutron scattering, [10][11][12] and NMR, [13][14][15][16] but no systematic study of M HS with M ϭNa, K, Rb, Cs to characterize the influence of symmetry and strength of the coordination potential on the dynamics of the anions has been presented. This paper is a part of a series [17][18][19][20] focusing on the structure and the dynamics in these compounds. We used powder 17 and single crystal 19 neutron diffraction, quasielastic neutron scattering, 18 and 1 H-NMR 20 to study the hydrogensulfides of sodium, potassium, and rubidium.…”

“…This paper is a part of a series [17][18][19][20] focusing on the structure and the dynamics in these compounds. We used powder 17 and single crystal 19 neutron diffraction, quasielastic neutron scattering, 18 and 1 H-NMR 20 to study the hydrogensulfides of sodium, potassium, and rubidium. In this paper we present results regarding the hydrogensulfide of cesium, including neutron and x-ray diffraction, calorimetric investigations, second moments (M 2 ) of the NMR proton absorption signal and the NMR spin-lattice relaxation times (T 1 ) of the protons.…”

Solid-State Ligand Dynamics in Interpenetrating Mn[N(CN)2]2(Pyrazine): A Neutron Spectroscopy Study

“…Within the time scale window available to neutron quasielastic scattering, 180°rotational jumps are rarely observed. Documented cases include the rotational motion of small anions such as hydrogensulfides 21 and the NH 2 unit in monoclinic potassium amide with a large activation energy of 185 meV and a correlation time of 33 ps at 324 K. 22 Two-fold jumps about a 4-fold axis have been observed in the much larger molecular system of cubane, whose orientational potential is mainly determined by van der Waals interactions. 14 In the present case, the relatively large volume available to each pyrazine in the interpenetrating lattice is sufficient to result in a low rotational barrier, allowing these large molecular fragments to rotate on the unusually short time scales observed here.…”

Reorientational disorder of anions in the hydrogen sulfides of sodium and potassium (NaDS and KDS) investigated by neutron diffraction between T=4 K and T=470 K

“…Many properties of the title compounds and NaOD/OH and KOD/OH are comparable: charge asymmetric anions, coordination sphere of the anions, and time scale (10 Ϫ12 s) of the reorientational motion of the anions. 24,28,44,45 …”