The open archive for STFC research publications

Full Record Details

Persistent URL http://purl.org/net/epubs/work/33937
Record Status Checked
Record Id 33937
Title Proton dynamics in lithium-ammonia solutions and expanded metals
Abstract Quasielastic neutron scattering has been used to study proton dynamics in the system lithium-ammonia at concentrations of 0, 4, 12, and 20 mole percent metal (MPM) in both the liquid and solid (expanded metal) phases. At 230 K, in the homogenous liquid state, we find that the proton self-diffusion coefficient first increases with metal concentration, from 5.6×10?5cm2s?1 in pure ammonia to 7.8×10?5cm2s?1 at 12 MPM. At higher concentrations we note a small decrease to a value of 7.0×10?5cm2s?1 at 20 MPM (saturation). These results are consistent with NMR data, and can be explained in terms of the competing influences of the electron and ion solvation. At saturation, the solution freezes to form a series of expanded metal compounds of composition Li(NH3)4. Above the melting point, at 100 K, we are able to fit our data to a jump-diffusion model, with a mean jump length (l) of 2.1 Å and residence time (?) of 3.1 ps. This model gives a diffusion coefficient of 2.3×10?5cm2s?1. In solid phase I (cubic, stable from 88.8 to 82.2 K) we find that the protons are still undergoing this jump diffusion, with l=2.0Å and ?=3.9ps giving a diffusion coefficient of 1.8×10?5cm2s?1. Such motion gives way to purely localized rotation in solid phases IIa (from 82.2 to 69 K) and IIb (stable from 69 to 25 K). We find rotational correlation times (?rot) of the order of 2.0 and 7.3 ps in phases IIa and IIb, respectively. These values can be compared with a rotational mode in solid ammonia with ?rot?2.4ps at 150 K.
Organisation CCLRC , ISIS , ISIS-IRIS
Keywords ISIS 2005 , ISIS 2005 Update , physics , chemistry
Funding Information
Related Research Object(s):
Licence Information:
Language English (EN)
Type Details URI(s) Local file(s) Year
Journal Article J Chem Phys 124 (2006): 024501. doi:10.1063/1.2145745 2006