Synthesis of organo-phosphorous species in space: the reaction of P+ with C2H2
Abstract
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
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BibTeX
@misc{michielan2026synthesis,
title = {{Synthesis of organo-phosphorous species in space: the reaction of P$^+$ with C$_2$H$_2$}},
author = {Matteo Michielan and Jorge Alonso de la Fuente and Roland Thissen and Christian Alcaraz and Nicolas Solem and Cristina Sanz Sanz and Susana Gómez Carrasco and Miroslav Polášek and Alexandre Zanchet and Marcelino Agúndez and Daniela Ascenzi},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.33657},
eprint = {2609.33657},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.33657},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Synthesis of organo-phosphorous species in space: the reaction of P^+ with C_2H_2
AU - Matteo Michielan
AU - Jorge Alonso de la Fuente
AU - Roland Thissen
AU - Christian Alcaraz
AU - Nicolas Solem
AU - Cristina Sanz Sanz
AU - Susana Gómez Carrasco
AU - Miroslav Polášek
AU - Alexandre Zanchet
AU - Marcelino Agúndez
AU - Daniela Ascenzi
PY - 2026
DA - 2026/09/27
PB - arXiv
DO - 10.48550/arxiv.2609.33657
UR - https://arxiv.org/abs/2609.33657
AB - 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 C_2H_2 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^+ + H_2 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
ER -