Searching for the elusive CH 2 + with the James Webb Space Telescope

Abstract

Context . Carbocations are key species in interstellar chemistry, providing entry points for building larger hydrocarbons. CH + , and more recently, CH 3 + , have been detected. Other carbocations await detection to provide a comprehensive view of the astrochemical network that is at work in the interstellar medium. Aims . We search for CH 2 + in objects in which CH 3 + was detected and evaluate the most favorable conditions for detecting the elusive CH 2 + reactive cation. Methods . We calculated the CH 2 + rotational and rovibrational transitions expected to contribute in the mid- to far-infrared, focusing on the lower-energy rovibrational levels. We then calculated CH 2 + 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 CH 3 + have already been detected. We used thermochemical models to predict the abundance and spatial morphology of CH 2 + to better understand its nondetection. Results . 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 CH 3 + in their excited states. Based on model calculations for photodissociation regions and assuming similar excitation temperatures, the upper limit derived from observations and CH 2 + 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 CH 2 + is key in providing observational constraints on astrochemical models.

Exploration of Exoplanet Atmospheres with the James Webb Space Telescope
Sasha Hinkley, David K. Sing
arXiv4 Sep 2026PreprintarXiv licenceFull textInstrumentation & methods Planetary science & exoplanetsarXiv
A New Era for Supernova Science with the James Webb Space Telescope
Justin Pierel, David Coulter, Christa DeCoursey +17
arXiv8 Oct 2026PreprintarXiv licenceFull textCosmologyarXiv
Strong Gravitational Lensing with the James Webb Space Telescope
Adi Zitrin
arXiv1 Sep 2026PreprintarXiv licenceFull textCosmology GalaxiesarXiv
Hydrocarbon Hazes on Temperate Sub-Neptune K2-18b Supported by Data from the James Webb Space Telescope
Ruohan Liu, Panayotis Lavvas, Giovanna Tinetti +3
The Astronomical Journal2 Jul 2026Peer-reviewedCC BY 4.0Full text1 citedSolar & stellar physicsHAL
Extragalactic Multi-Band Exploration of Red Supergiants (EMBERS): Pipeline, Source Classification, and Bolometric Properties of 101,219 Red Supergiants from James Webb Space Telescope Imaging
Aswin Suresh, Charles D. Kilpatrick, Wen-fai Fong +6
arXiv16 Sep 2026PreprintCC BY 4.0Full textGalaxies Solar & stellar physicsarXiv

Cite

BibTeX RIS

BibTeX

@article{zannese2026searching,
  title = {{Searching for the elusive CH 2 + with the James Webb Space Telescope}},
  author = {M. Zannese and L H Coudert and E. Dartois and P. Dell’ova and O. Roncero and P. del Mazo-Sevillano and U. Jacovella and B. Gans and J R Goicoechea and D. van de Putte and C. Boersma and E. Habart and E. Peeters and J. Cami and R. Chown and I. Schroetter and O. Kannavou},
  journal = {Astronomy \& Astrophysics - A\&A},
  year = {2026},
  month = aug,
  doi = {10.1051/0004-6361/202660602},
  url = {https://hal.science/hal-05780139v1},
  note = {CC BY 4.0},
}

RIS

TY  - JOUR
TI  - Searching for the elusive CH 2 + with the James Webb Space Telescope
AU  - M. Zannese
AU  - L H Coudert
AU  - E. Dartois
AU  - P. Dell’ova
AU  - O. Roncero
AU  - P. del Mazo-Sevillano
AU  - U. Jacovella
AU  - B. Gans
AU  - J R Goicoechea
AU  - D. van de Putte
AU  - C. Boersma
AU  - E. Habart
AU  - E. Peeters
AU  - J. Cami
AU  - R. Chown
AU  - I. Schroetter
AU  - O. Kannavou
PY  - 2026
DA  - 2026/08/11
JO  - Astronomy & Astrophysics - A&A
DO  - 10.1051/0004-6361/202660602
UR  - https://hal.science/hal-05780139v1
AB  - Context . Carbocations are key species in interstellar chemistry, providing entry points for building larger hydrocarbons. CH + , and more recently, CH 3 + , have been detected. Other carbocations await detection to provide a comprehensive view of the astrochemical network that is at work in the interstellar medium. Aims . We search for CH 2 + in objects in which CH 3 + was detected and evaluate the most favorable conditions for detecting the elusive CH 2 + reactive cation. Methods . We calculated the CH 2 + rotational and rovibrational transitions expected to contribute in the mid- to far-infrared, focusing on the lower-energy rovibrational levels. We then calculated CH 2 + 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 CH 3 + have already been detected. We used thermochemical models to predict the abundance and spatial morphology of CH 2 + to better understand its nondetection. Results . 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 CH 3 + in their excited states. Based on model calculations for photodissociation regions and assuming similar excitation temperatures, the upper limit derived from observations and CH 2 + 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 CH 2 + is key in providing observational constraints on astrochemical models.
SN  - 0004-6361
SN  - 1432-0746
ER  -

Abstract

Related

Cite