The chemistry of phosphorus-bearing molecules under energetic phenomena
  For decades, the detection of phosphorus-bearing molecules in the
interstellar medium was restricted to high-mass star-forming regions (as e.g.
SgrB2 and Orion KL) and the circumstellar envelopes of evolved stars. However,
recent higher-sensitivity observations have revealed that molecules such as PN
and PO are present not only toward cold massive cores and low-mass star-forming
regions with PO/PN ratios >1, but also toward the Giant Molecular Clouds in the
Galactic Center known to be exposed to highly energetic phenomena such as
intense UV radiation fields, shock waves and cosmic rays. In this paper, we
carry out a comprehensive study of the chemistry of phosphorus-bearing
molecules across different astrophysical environments which cover a range of
physical conditions (cold molecular dark clouds, warm clouds, hot cores/hot
corinos) and are exposed to different physical processes and energetic
phenomena (proto-stellar heating, shock waves, intense UV radiation and cosmic
rays). We show how the measured PO/PN ratio (either >1 as in e.g. hot molecular
cores, or <1 as in UV strongly illuminated environments) can provide
constraints on the physical conditions and energetic processing of the source.
We propose that the reaction P + OH --> PO + H, not included in previous works,
could be an efficient gas-phase PO formation route in shocks. Our modelling
provides a template with which to study the detectability of P-bearing species
not only in regions in our own Galaxy but also in extragalactic sources.
