Determine the dissociative-recombination rate of PO⁺
Determine the dissociative-recombination rate coefficient of PO⁺, particularly under the extreme physical conditions of supernova-remnant shocks, to improve models of phosphorus chemistry and the PO⁺/PN abundance ratio.
References
As already stated by , the adopted value is an educated guess and no dedicated studies are available to date. However, the abundances of molecular ions in highly-ionised environments such as SNRs can be strongly affected by the adopted dissociative recombination rates \citep[e.g.][]{priestley2017}. We find that already by reducing the \citet{thorne1984} value by a factor of ten, PO$+$/PN ratios greater than unity can be produced during the post-shock refreezing period ($\sim$10$4$ yr), as shown in Figure \ref{fig:lodr}. For comparison, previous shock modelling suggests characteristic interaction timescales larger than $104$ yr for W44 and $103$ yr for IC443 \citep[e.g.][]{cosentino2019,reach2019}. However, we note that these value are highly uncertain. Future efforts are needed to obtain a more accurate estimate of this reaction rate in studies of phosphorus chemistry, particularly in extreme environments such as SNR shocks.