The molecular chemistry of Type Ibc supernovae, and diagnostic potential
  with the James Webb Space Telescope
  A currently unsolved question in supernova research is the origin of
stripped-envelope supernovae (SESNe). Such SNe lack spectral signatures of
hydrogen (Type Ib), or hydrogen and helium (Type Ic), indicating that the outer
stellar layers have been stripped during their evolution. The mechanism for
this is not well understood, and to disentangle the different scenarios
determination of nucleosynthesis yields from observed spectra can be attempted.
However, the interpretation of observations depends on the adopted spectral
models. A previously missing ingredient in these is the inclusion of molecular
effects, which can be significant. We aim to investigate how the molecular
chemistry in stripped-envelope supernovae affects physical conditions and
optical spectra and produces ro-vibrational emission in the mid-infrared (MIR).
We also aim to assess the diagnostic potential of observations of such MIR
emission with JWST. We couple a chemical kinetic network including carbon,
oxygen, silicon, and sulfur-bearing molecules into the NLTE spectral synthesis
code SUMO. We let four species - CO, SiO, SiS and SO - participate in the NLTE
cooling of the gas to achieve self-consistency between the molecule formation
and the temperature. We apply the new framework to model the spectrum of a Type
Ic supernova in the 100-600d time range. Molecules are predicted to form in
SESN ejecta in significant quantities (typical mass $10^{-3}$ $M_\odot$)
throughout the 100-600d interval. The impact on the temperature and optical
emission depends on the density of the oxygen zones and varies with epoch. For
example, the [O I] 6300, 6364 feature can be quenched by molecules from 200 to
450d depending on density. The MIR predictions show strong emission in the
fundamental bands of CO, SiO, and SiS, and in the CO and SiO overtones.
