Collisional excitation of cyclopentadiene by helium
Year: 2026
Type: article
Abstract: Context . Complex organic molecules, including large cyclic species, are prevalent in interstellar space and play a key role in various astrochemical processes. Cyclopentadiene (c-C 5 H 6 ) is a five-membered cyclic hydrocarbon recently detected in TMC-1 and some other interstellar molecular clouds. While accurate spectroscopic data are available, collisional rate coefficients for its rotational transitions are missing so far, introducing a potential limitation in the interpretation of observations. Aims . The aim of this study is to provide a comprehensive set of state-to-state thermal rate coefficients for the rotational excitation of c-C 5 H 6 due to collisions with helium, crucial for non-local thermodynamic equilibrium (non-LTE) radiative transfer modelling in astrophysical environments, and to examine how far the molecule is from thermalisation under the physical conditions of cold molecular clouds. Methods . The research employed accurate quantum scattering calculations using the close coupling (CC) and coupled states (CS) methods, based on a highly correlated three-dimensional potential energy surface for the [c-C 5 H 6 -He] collisional complex. Calculations were performed for a wide range of rotational states (from j = 0 to j ≤ 25) and kinetic temperatures (from 10 to 50 K). Results . We calculated a complete set of thermal rate coefficients for both ortho and para nuclear spin configurations of c-C 5 H 6 . Radiative transfer simulations demonstrated that most rotational levels of cyclopentadiene are fully thermalised under typical cold cloud conditions and exhibit minor non-LTE effects. Nevertheless, this study is among the firsts to utilise accurate state-to-state rate coefficients for a radiative transfer simulation of a large cyclic species detected in space. This allowed us to draw some general conclusions and paves the way for future collisional excitation studies of complex astromolecules that will enable a more precise interpretation of upcoming detections.
Source: Astronomy and Astrophysics
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
Funders: Ministerio de Ciencia, Innovación y Universidades, European Cooperation in Science and Technology, Centre National d’Etudes Spatiales, Centre National de la Recherche Scientifique, Institut Universitaire de France, Grand Équipement National De Calcul Intensif, HORIZON EUROPE Framework Programme, European Research Council, Agencia Estatal de Investigación, H2020 European Research Council, HORIZON EUROPE Marie Sklodowska-Curie Actions
Awards: G1152523013, G1274526653, G185641531, G1953443719, G1989168376, G2162647311, G2262748287, G2911857317, G3443738222, G3480869486, G4042206520, Collisional excitation of interstellar molecules: towards reactive systems, G425668148, G4515945706, G464105488, G7084143925, VIBrational and Rotational Excitation in Astronomically relevant molecular Collisions, G8684520763, G8701456514, G8976216650
OpenAlex ID: W7206214365