The intermolecular structure and dynamics of an acidic 1-ethyl-3-methylimidazolium fluoride-hydrogen fluoride solution ([emim][F]center dot 2.3HF) have been studied through a Car-Parrinello molecular dynamics simulation. The calculated structure factor is found to be in good agreement with X-ray scattering data. The solution consists of [emim] cations and polyfluoride anions of the kind F(HF)(n)(-). With increasing n, the length of the H-F covalent bond in the polyfluoride species is found to decrease, with a concomitant blue shift in the frequency of its stretching mode. Evidence for the presence of a hydrogen bond between the acidic ring hydrogen of the cation and the fluoride ion is presented.