Searching for the elusive CH 2 + with the James Webb Space Telescope
Year: 2026
Type: article
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.
Source: Astronomy and Astrophysics
Institutions: Centre National de la Recherche Scientifique, Consejo Superior de Investigaciones Científicas, Université Paris-Saclay, Instituto de Física Fundamental, Institut d'Astrophysique Spatiale, Institut des Sciences Moléculaires d'Orsay, Universidad de Salamanca, Western University, Space Telescope Science Institute, Ames Research Center, Search for Extraterrestrial Intelligence, The Ohio State University, Institut de Planétologie et d'Astrophysique de Grenoble, Université Grenoble Alpes
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
Funders: National Aeronautics and Space Administration, Space Telescope Science Institute, San José State University, Agence Nationale de la Recherche, Centre National d’Etudes Spatiales, Centre National de la Recherche Scientifique, Ames Research Center, Canadian Space Agency, Natural Sciences and Engineering Research Council of Canada, Agencia Estatal de Investigación, European Social Fund
OpenAlex ID: W7166646060