The local environment of CS2 and in solution in two ionic liquids ([C1C1im][NTf2] and [C4C1im][NTf2]) are investigated by atomistic simulation and compared with that in neat CS2. The intermolecular vibrational densities of states of CS2 are calculated and compared with experimental OHD-RIKES spectra. The fair agreement of the results from solutions but poor agreement of the results from neat CS2 suggest that while collective effects are unimportant in solutions, they have a major effect on the OHD-RIKES spectrum of neat CS2. Comparing polarizable and unpolarizable models for CS2 emphasizes the importance of polarizability in determining local structure.