Collective dynamics of liquid acetone investigated by inelastic X-ray scattering

Abstract The dynamic structure factors S(Q, ω) of liquid acetone were measured in a wide Q range 1.9–41.2 nm−1 with a high-resolution inelastic X-ray scattering (IXS) spectrometer installed at BL35XU of the SPring-8. Highly damped collective excitations of the longitudinal acoustic (LA) phonons are observed. The IXS spectra were analyzed by using a generalized Langevin formalism with the help of a sparse modeling to deduce reasonable Q dependences of the fitting parameters. The dispersion relation of the LA phonon excitations shows a highly positive deviation by about 65% from the adiabatic velocity of sound, which is larger than that in non-polar liquids such as CCl4 and benzene with van der Waals interactions, due probably that the acetone is a polar liquid. Microscopic dynamic parameters, such as viscoelastic relaxation rates and viscosity, are discussed by comparing with existing macroscopic dynamic properties. The fast and slow viscoelastic relaxations correspond to the vibration dynamics and reorientation correlations, respectively.