[astro-ph.GA] Carbocations are key species in interstellar chemistry, providing entry points for building larger hydrocarbons. CH+, and more recently, CH3+, have been detected. Other carbocations await detection to provide a comprehensive view of the astrochemical network that is at work in the interstellar medium.
We search for CH2+ in objects in which CH3+ was detected and evaluate the most favorable conditions for detecting the elusive CH2+ reactive cation. We calculated the CH2+ rotational and rovibrational transitions expected to contribute in the mid- to far-infrared, focusing on the lower-energy rovibrational levels.
We then calculated CH2+ infrared emission spectra at different excitation temperatures and compared them to JWST spectra of the externally irradiated disk d203-506 in Orion, where CH+ and CH3+ have already been detected.
We used thermochemical models to predict the abundance and spatial morphology of CH2+ to better understand its nondetection. The comparison to JWST spectra allowed us to provide excitation-temperature-dependent upper limits to the excited column density. These are several times lower than those detected for CH+ and CH3+ in their excited states.
Based on model calculations for photodissociation regions and assuming similar excitation temperatures, the upper limit derived from observations and CH2+ model spectrum is either slightly above or below the column density expected from models of photodissociation regions.
We provide a list of tabulated transitions to allow the community to search for this carbocation in future observations as CH2+ is key in providing observational constraints on astrochemical models.
M. Zannese, L. H. Coudert, E. Dartois, P. Dell’Ova, O. Roncero, P. del Mazo-Sevillano, U. Jacovella, B. Gans, J. R. Goicoechea, D. Van De Putte, C. Boersma, E. Habart, E. Peeters, J. Cami, R. Chown, I. Schroetter, O. Kannavou
Comments: Accepted to A&A on the 16/06/2026
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2607.01155 [astro-ph.GA] (or arXiv:2607.01155v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2607.01155
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Submission history
From: Marion Zannese
[v1] Wed, 1 Jul 2026 16:39:36 UTC (2,830 KB)
https://arxiv.org/abs/2607.01155
Astrobiology, Astrochemistry, interstellar,
