Rotational Excitation Cross Sections for Chloronium Based on a New 5D Interaction Potential with Molecular Hydrogen.

Chloronium (HCl) is an important intermediate of Cl-chemistry in space. The accurate knowledge of its collisional properties allows a better interpretation of the corresponding observations in interstellar clouds and, therefore, a better estimation of its abundance in these environments. While the ro-vibrational spectroscopy of HCl is well-known, the studies of its collisional excitation are rather limited and these are available for the interaction with helium atoms only.

First close-coupling study of the excitation of a large cyclic molecule: collision of c-CH with He.

Recent astronomical observations revealed an increasing molecular complexity in the interstellar medium through the detection of a series of large cyclic carbon species. To correctly interpret these detections, a complex analysis is necessary that takes into account the non-local thermodynamic equilibrium (non-LTE) conditions of the emitting media ( when energy level populations deviate from a Boltzman distribution). This requires proper state-to-state collisional data for the excitation and de-excitation processes of the molecular levels.