The reaction of P+ with H_2O (D_2O): A pathway for the formation of PO and PO+ in the interstellar medium and circumstellar envelopes

Interstellar phosphorus shows uncertain depletion patterns and an unidentified main reservoir, with only a few P-bearing molecules detected despite their key astrochemical and astrobiological relevance. In particular, recent observations of with a high abundance with respect to PO suggest that ion–molecule chemistry may play a crucial role, motivating a reassessment of its formation pathways in the interstellar medium (ISM) and circumstellar envelopes. PO+ The role of the reaction between and water ( ) for the synthesis of and is explored in a joint experimental and theoretical study. Furthermore, new possible routes leading to the conversion of i) into PO (via a non-dissociative proton transfer reaction with ammonia) and of ii) PO into PN (via the adiabatic barrierless reaction of N(4S) with PO are proposed. P+ D2O PO+ POH+ POH+ The reaction plus was studied experimentally by measuring absolute cross-sections (CSs) and branching ratios (BRs), as a function of collision energy. Experiments were supported by a theoretical investigation combining high-level electronic structure calculations of the multidimensional triplet and singlet potential energy surfaces with a kinetic investigation to derive BRs and channel-specific rate constants as a function of temperature in the 10-5000 K range. P+ D2O The reaction + leads mostly to plus D (BR=90%), with plus being a minor channel (BR=10%). From the total reaction CS as a function of collision energy, estimates for the rate constant as a function of temperature have been obtained, with values ranging from 1.2 P+ D2O POD+ PO+ D2 cm3s^-1 (at 10 K) to 7.5 (at 5000 K). The proton transfer reactions between and is found to be efficient with rate constants in the range of 1.1-2.7 . cm^3s^ -1 POH^+ NH3 cm3s⁻1 molecule^ -1 The reaction of with water should be considered in astrochemical models in which phosphorus can be released in the gas phase as a cation, from the energetic processing of icy interstellar grains due to shocks. The reaction leads to as the main reaction product and relevant interstellar isomer, an important precursor for PO formation not only via dissociative recombination with electrons, but also by proton transfer to . The direct formation of as a secondary channel can explain the high / ratio detected in the ISM. P+ POH+ NH3 PO+ PO+ PO