Experimental study of the removal of excited state phosphorus atoms by H2O and H2: implications for the formation of PO in stellar winds

Abstract

The reactions of the low-lying metastable states of atomic phosphorus, P(2D) and P(2P), with H2O and H2 were studied by the pulsed laser photolysis at 248 nm of PCl3, combined with laser induced fluorescence detection of P(2D), P(2P) and PO. Rate coefficients between 291 and 740 K were measured, along with a yield for the production of PO from P(2D or 2P) + H2O of (35 ± 15)%. H2 reacts with both excited P states relatively efficiently; physical (i.e. collisional) quenching, rather than chemical reaction to produced PH + H, is shown to be the more likely pathway. A comprehensive phosphorus chemistry network is then developed using a combination of electronic structure theory calculations and a Master Equation treatment of reactions taking place over complex potential energy surfaces. The resulting model shows that at the high temperatures within two stellar radii of a MIRA variable AGB star in oxygen-rich conditions, collisional excitation of ground-state P(4S) to P(2D), followed by reaction with H2O, is a significant pathway for producing PO (in addition to the reaction between P(4S) and OH). The model also demonstrates that the PN fractional abundance in a steady (non-pulsating) outflow is under-predicted by about 2 orders of magnitude. However, under shocked conditions where sufficient thermal dissociation of N2 occurs at temperatures above 4000 K, the resulting N atoms convert a substantial fraction of PO to PN.

Phosphine reactivity and its implications for pyrolysis experiments and astrochemistry

“…As ALMA and Rosina teams proposed [9], PH 3 can suffer sequential dissociations in the presence of UV radiation, forming P atoms (Figure 1). Phosphorus atoms can collide with another species, leading to PO or PN molecules previously detected in other systems [4,26,30,31,66]. Or can condensate, forming solid phosphorus particles, as observed in Jupiter's atmosphere [67].…”

“…Douglas et al [30] proposed an update in the reaction network involving P-bearing species. The network includes the formation of PH that can form PH 3 by successive H addition.…”

“…Despite the molecules' simplicity, phosphorus compounds' chemistry continues to be unknown to those interested in the astrochemistry and astrobiology fields. Until now, few theoretical studies described the PO and PN reactions in ISM conditions [27][28][29][30][31][32]. While the PH 3 decomposition paths were investigated at higher temperatures to elucidate the epitaxy and vapor deposition mechanism [33][34][35].…”

Phosphine Reactivity and Its Implications for Pyrolysis Experiments and Astrochemistry

“…Douglas et al proposed an update in the P-bearing species reaction network. The network includes the formation of PH that can form PH 3 by successive H addition.…”

“…Despite the molecules’ simplicity, phosphorus compounds’ chemistry continues to be unknown to those interested in the astrochemistry and astrobiology fields. To date, few theoretical studies described the PO and PN reactions in ISM conditions. ,− At the same time, the PH 3 decomposition paths were investigated at higher temperatures to elucidate the epitaxy and vapor deposition mechanism. − In parallel, Semenov et al studied the PN rovibronic spectra theoretically by ab initio methods, which is pivotal to helping the correct identification of this molecule by experimental means. Due to these reasons, the present study aims to investigate the pathways for the formation and decomposition of PH 3 and the reactions that may form PO and PN beyond Earth by quantum chemistry methods.…”