Tracing the sources of cosmic rays with molecular ions
  The rate of ionization by cosmic rays in interstellar gas directly associated
with gamma-ray emitting supernova remnants is for the first time calculated to
be several orders of magnitude larger than the Galactic average. Analysis of
ionization-induced chemistry yields the first quantitative prediction of the
astrophysical H_{2}^{+} emission line spectrum, which should be detectable
together with H_3^+ lines. The predicted coincident observation of those
emission lines and gamma-rays will help prove that supernova remnants are
sources of cosmic rays.
