The P(4S) + NH(3Σ-) and N(4S) + PH(3Σ-)reactions as sources of interstellar phosphorus nitride
Abstract
Phosphorus nitride (PN) is believed to be one of the major reservoirs of phosphorus in the interstellar medium (ISM). For this reason, understanding which reactions produce PN in space and predicting their rate coefficients is important for modelling the relative abundances of P-bearing species and clarifying the role of phosphorus in astrochemistry. In this work, we explore the potential energy surfaces of the $\textrm{P}(^4\textrm{S}) + \textrm{NH}(^3Σ^-)$ and $\textrm{N}(^4\textrm{S}) + \textrm{PH}(^3Σ^-)$ reactions and the formation of $\textrm{H}(^2\textrm{S}) + \textrm{PN}(^1Σ^+)$ through high accuracy ab initio calculations and the variable reaction coordinate transition state theory (VRC-TST). We found that both reactions proceed without an activation barrier and with similar rate coefficients that can be described by a modified Arrhenius equation ( $k(T)=α\!\left( T/300 \right)^{β} \exp\!{(\!-\!γ/T)})$ with $α=0.93× 10^{-10}cm^3 s^{-1}$ , $β=-0.18$ and $γ=0.24 K$ for the $\textrm{P} + \textrm{NH} \longrArr \textrm{H} + \textrm{PN}$ reaction and $α=0.88× 10^{-10}cm^3 s^{-1}$ , $β=-0.18$ and $γ=1.01 K$ for the $\textrm{N} + \textrm{PH} \longrArr \textrm{H} + \textrm{PN}$ one. Both reactions are expected to be relevant for modelling PN abundances even in the cold environments of the ISM. Given the abundance of hydrogen in space, we have also predicted rate coefficients for the destruction of PN via H + PN collisions.
- Publication:
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Publications of the Astronomical Society of Australia
- Pub Date:
- March 2023
- DOI:
- 10.1017/pasa.2023.13
- Bibcode:
- 2023PASA...40...11G
- Keywords:
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- interstellar medium;
- molecular data;
- molecular reactions;
- chemical kinetics;
- theoretical data