An inelastic neutron scattering and molecular dynamics simulation study of the interaction properties of liquid CO2 is reported. By means of an interaction-based interpretation of neutron scattering and simulation results for the dynamic structure factor we also show that (CO2)(2) equilibrium dimers characteristic of the gas phase are present in dense liquid carbon dioxide and predominantly contribute to the observed picosecond dynamics. Such a memory of the gas-phase structures was not observed in liquid methane. The role of anisotropy and strength of interactions on these important differences is discussed. (C) 2008 Elsevier B.V. All rights reserved.