Water dynamics in a lithium chloride aqueous solution probed by Brillouin neutron and x-ray scattering

We studied the collective excitations in an aqueous solution of lithium chloride over the temperature range of 270-205K using neutron and x-ray Brillouin scattering. Both neutron and x-ray experiments revealed the presence of low-and high-frequency excitations, similar to the low-and high-frequency excitations in pure water. These two excitations were detectable through the entire temperature range of the experiment, at all probed values of the scattering momentum transfer (0.2 Å ^-1 < Q < 1.8Å ^-1). A wider temperature range was investigated using elastic intensity neutron and x-ray scans. Clear evidence of the crossover in the dynamics of the water molecules in the solution was observed in the single-particle relaxational dynamics on the νeV (nanosecond) time scale, but not in the collective dynamics on the meV (picosecond) time scale.