Photodissociation of [Fex(C₂₄H₁₂)y]⁺ complexes in the PIRENEA setup: iron-polycyclic aromatic hydrocarbon clusters as candidates for very small interstellar grains.
Abstract
Astronomical observations suggest that polycyclic aromatic hydrocarbons (PAHs) that emit at the surface of molecular clouds in the interstellar medium are locally produced by photodestruction of very small grains (VSGs). In this paper, we investigate [Fex(PAH)y]⁺ clusters as candidates for these VSGs. [FeC₂₄H₁₂]⁺ and [Fex(C₂₄H₁₂)₂]⁺ (x = 1-3) complexes were formed by laser ablation of a solid target in the PIRENEA setup, a cold ion trap dedicated to astrochemistry. Their photodissociation was studied under continuous visible irradiation. Photodissociation pathways are identified and characteristic time scales for photostability are provided. [Fex(C₂₄H₁₂)₂]⁺ (x = 1-3) complexes sequentially photodissociate by losing iron atoms and coronene units under laboratory irradiation conditions with C₂₄H₁₂⁺ as the smallest photofragment. The study of the dissociation kinetics gives interesting insights into the structures of the complexes. The dissociation rate is found to increase with the complex size. Density functional theory (DFT) and time-dependent DFT calculations show that the increase of the number of Fe atoms leads to an increased stability of the complex but also to an increased heating rate in the experimental conditions, due to the presence of strong electronic excitations in the visible. The modeling of the dissociation kinetics of the smallest complex [FeC₂₄H₁₂]⁺ by using a kinetic Monte Carlo code allows derivation of the dissociation parameters and the internal energy for this complex, showing in particular that it could dissociate under interstellar irradiation conditions. First insights into the dissociation of larger complexes in these conditions are also given.
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BibTeX
@article{simon2026photodissociation,
title = {{Photodissociation of [Fex(C₂₄H₁₂)y]⁺ complexes in the PIRENEA setup: iron-polycyclic aromatic hydrocarbon clusters as candidates for very small interstellar grains.}},
author = {Aude Simon and Christine Joblin},
journal = {Journal of Physical Chemistry A},
year = {2026},
month = nov,
doi = {10.1021/jp8099785},
url = {https://hal.science/hal-00843007v1},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - JOUR
TI - Photodissociation of [Fex(C₂₄H₁₂)y]⁺ complexes in the PIRENEA setup: iron-polycyclic aromatic hydrocarbon clusters as candidates for very small interstellar grains.
AU - Aude Simon
AU - Christine Joblin
PY - 2026
DA - 2026/11/03
JO - Journal of Physical Chemistry A
DO - 10.1021/jp8099785
UR - https://hal.science/hal-00843007v1
AB - Astronomical observations suggest that polycyclic aromatic hydrocarbons (PAHs) that emit at the surface of molecular clouds in the interstellar medium are locally produced by photodestruction of very small grains (VSGs). In this paper, we investigate [Fex(PAH)y]⁺ clusters as candidates for these VSGs. [FeC₂₄H₁₂]⁺ and [Fex(C₂₄H₁₂)₂]⁺ (x = 1-3) complexes were formed by laser ablation of a solid target in the PIRENEA setup, a cold ion trap dedicated to astrochemistry. Their photodissociation was studied under continuous visible irradiation. Photodissociation pathways are identified and characteristic time scales for photostability are provided. [Fex(C₂₄H₁₂)₂]⁺ (x = 1-3) complexes sequentially photodissociate by losing iron atoms and coronene units under laboratory irradiation conditions with C₂₄H₁₂⁺ as the smallest photofragment. The study of the dissociation kinetics gives interesting insights into the structures of the complexes. The dissociation rate is found to increase with the complex size. Density functional theory (DFT) and time-dependent DFT calculations show that the increase of the number of Fe atoms leads to an increased stability of the complex but also to an increased heating rate in the experimental conditions, due to the presence of strong electronic excitations in the visible. The modeling of the dissociation kinetics of the smallest complex [FeC₂₄H₁₂]⁺ by using a kinetic Monte Carlo code allows derivation of the dissociation parameters and the internal energy for this complex, showing in particular that it could dissociate under interstellar irradiation conditions. First insights into the dissociation of larger complexes in these conditions are also given.
SN - 1089-5639
SN - 1520-5215
ER -