We probe the linear optical properties of the neat liquid acetonitrile (CH3CN) at ambient conditions using all initio density functional theory. Uncorrelated structures extracted from Monte Carlo simulation are employed to efficiently calculate average electronic properties. It become,, evident that condensation leads to a conduction band with a large degree of dispersion, which is consistent with the description of dipolar liquids. This allows an interpretation of the dielectric spectrum based on the electronic structure of liquid CH3CN, and clearly shows the influence of intermolecular interactions in the absorption features. We find that the lowest-lying excitation of the condensed phase occurs at 7.8 eV, which is reasonable as compared to the 8-9.5 eV absorption region measured in the gas phase.