![Absolute CSs for the reaction of P+ with C2H2, measured at ECM = 0.14 eV as a function of the photon energy. Products are detected at m/z 56 (HCCP+, orange triangles) and m/z 55 (CCP+, blue circles). From Ephot ≈23 eV an additional product is observed at m/z 26 (C2H2 +, black squares). The vertical dashed black line indicates Ephot value at which CS trends as a function of ECM have been measured. Grey and red arrows indicate the calculated thermodynamic thresholds for production of P+ in ground and excited states, as detailed in the text.-- [astro-ph.SR]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/10/Synthesis.png?fit=1200%2C674&ssl=1)
[astro-ph.SR] Despite its low cosmic abundance, phosphorus is a bioessential element whose prebiotic availability and incorporation into biomolecules remain open questions. Only a few phosphorous containing molecules with P to C bonds have been detected in astronomical environments (CP, CCP, HCP).
More complex species have been proposed, but their formation and destruction pathways remain poorly constrained. Gas-phase ion molecule chemistry involving P cations may contribute to organophosphorus formation, particularly in protostellar shocks and outflows, while reactions of ground state P cations with closed-shell neutrals provide benchmarks for spin-forbidden mechanisms.
We investigate the reaction of P+ with C2H2 through a joint experimental and theoretical study aimed at revising astrochemical database rate coefficients. Absolute cross sections and branching ratios were measured as a function of collision energy and complemented by high-level electronic structure calculations and a refined capture model accounting for higher-order long-range interactions and intermediate complex formation. Channel-specific rate coefficients were derived in the range from 10 to 5000 K.
The reaction produces predominantly HCCP++ H (branching ratio 99%), while CCP++ H2 is a minor channel (branching ratio 1%) arising from intersystem crossing from the triplet to the singlet potential energy surfaces. The total rate coefficient at 300 K agrees well with the SIFT value, but it increases with decreasing temperature, deviating from a pure Langevin trend.
The reaction should be included in astrochemical models where phosphorus is released as P+, such as during energetic processing of icy grains in shocks. It provides a pathway to linear HCCP+, a potentially relevant precursor to the observed CP and CCP species through dissociative recombination
Matteo Michielan, Jorge Alonso de la Fuente, Roland Thissen, Christian Alcaraz, Nicolas Solem, Cristina Sanz Sanz, Susana Gómez Carrasco, Miroslav Polášek, Alexandre Zanchet, Marcelino Agúndez, Daniela Ascenzi
Comments: 22 pages, 6 figures, 1 Appendix, submitted to A&A
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2609.33657 [astro-ph.SR](or arXiv:2609.33657v1 [astro-ph.SR] for this version)
https://doi.org/10.48550/arXiv.2609.33657
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Submission history
From: Daniela Ascenzi PhD
[v1] Sun, 27 Sep 2026 15:19:45 UTC (5,573 KB)
https://arxiv.org/abs/2609.33657
Astrobiology, Astrochemistry,
