ACA observation and chemical modelling of phosphorus nitride (PN) towards the hot molecular cores G10.47+0.03 and G31.41+0.31

Phosphorus (P) is one of the important elements for the formation of life and plays a crucial role in several biochemical processes. Recent spectral line surveys have confirmed the existence of P-bearing molecules, especially PN and PO, in the star-formation regions, but their formation mechanisms are poorly understood. The P-bearing molecule phosphorus nitride (PN) is detected in several star-forming regions, but this molecule has been poorly studied at high gas densities ($\ge$10${}^6$ cm${}^{-3}$) hot molecular cores. In this article, we present the detection of the rotational emission line of PN with transition J = 3$-$2 towards the hot molecular cores G10.47+0.03 and G31.41+0.31, using the Atacama Compact Array (ACA). The estimated column densities of PN for G10.47+0.03 and G31.41+0.31 using the local thermodynamic equilibrium (LTE) model are (3.60$\pm$0.2)$\times$10${}^{13}$ cm${}^{-2}$ and (9.10$\pm$0.1)$\times$10${}^{12}$ cm${}^{-2}$ with an excitation temperature of 150$\pm$25 K. The fractional abundance of PN relative to H${}_2$ is 2.76$\times$10${}^{-10}$ for G10.47+0.03 and 5.68$\times$10${}^{-11}$ for G31.41+0.031. We compute the two-phase warm-up chemical model of PN to understand the chemical evolution in the environment of hot molecular cores. After chemical modelling, we claim that PN is created in the gas phase via the neutral-neutral reaction between PO and N in the warm-up stage. Similarly, PN is destroyed via the ion-neutral reaction between H${}_3$O${}^{+}$ and PN.