Phosphine reactivity and its implications for pyrolysis experiments and astrochemistry

Despite the importance of phosphorus-bearing molecules for life and their abundance outside Earth, the chemistry of those compounds still is poorly described. The present study investigated phosphine (PH3) decomposition and formation pathways. The reactions studied include phosphine thermal dissociation, conversion into PO, PN, and reactions in the presence of H2O+. The thermodynamic and rate coefficients of all reactions were calculated in the range of 50 – 2000 K considering the CCSD(T)/6-311G(3df,3pd)//B97xD/6-311G(3df,3pd) electronic structure data. The rate coefficients were calculated by RRKM and SCTST theories. According to the results, PH3 is stable due to thermal decomposition at T < 100 K but can be formed promptly by a reaction mechanism involving PH, PO, and PN. In the presence of radiation or ions, PH3 is readily decomposed. For this reason, it should be mainly associated with dust grains or icy mantles to be observed. The intersystem crossing associated with the dissociation of the isomers PON, NPO, and PNO was accessed by multireference methods, and its importance for the gas-phase PH3 formation/destruction was discussed. Also, the impact of the present outcomes on the phosphorus space chemistry was highlighted.