  We present and evaluate an efficient method for simulating Raman spectra from
molecular dynamics (MD) calculations {\it without} defining normal modes. We
apply the method to high pressure hydrogen in the high-temperature "Phase IV":
a plastic crystal in which the conventional picture of fixed phonon eigenmodes
breaks down.
  Projecting trajectories onto in-phase molecular stretches is shown to be many
orders of magnitude faster than polarisability calculations, allowing
statistical averaging at high-temperature.
  The simulations are extended into metastable regimes and identify several
regimes associated with symmetry-breaking on different timescales, which are
shown to exhibit features in the Raman spectra at the current experimental
limit of resolvability. In this paper we have concentrated on the methodology,
a fuller description of the structure of Phase IV hydrogen is given in a
previous paper
