The role of inelasticity in cold molecular anions encounters

The possible existence of molecular anions in the interstellar medium was put forward more than thirty years ago. Currently, anionic species in the interstellar space have been confirmed to be present under different conditions and in significant abundances, so that molecular anions are considered to be at play in the physical and chemical evolution of several astronomical environments like cold, dense and diffuse molecular clouds. The general focus of this project concerns a computational investigation, on the basis of the quantum scattering theory, of collisions between astrophysically important molecular anions (like CC-, CCH-, CN-, NCO-) and atomic helium (He) or atomic/molecular hydrogen (H/H2), the latter being among the most abundant species in cold regions of the interstellar medium. This kind of theoretical and computational investigation will be helpful in clarifying how efficiently the translational energy of the chemical projectile (He, H or H2) gets redistributed among the translational energy and the internal (rotational) energy of the above four anions. In line with the above general focus, a detailed study of the angular translational redistribution of the two species which enter the collisional process will be also carried out.

Decades after the possible existence of molecular anions in the interstellar medium was put forward, currently several anionic species in the interstellar space have been confirmed to exist under different conditions and in significant relative abundances, so that molecular anions are considered to be at play in the physical and chemical evolution of several astronomical environments like cold, dense and diffuse molecular clouds. The general focus of the project concerned an accurate computational investigation of the interaction between small molecular anions like CN- (the smallest detected molecular anion) and CC- (not yet observed, but considered a species likely existent in specific regions of the interstellar medium) and He/H2, and of their inelastic collisions at low temperature. Generally speaking, the physics at the nanoscopic level can be concentrated in a very important parameter named rate constant, which depends of the temperature. The findings about the CN- allowed for an accurate comparison between the rate constants for this anion involved in low-energy collisions either with He and H2, when the latter is in its lowest internal state which is non-rotating. The obtained findings helps in disproving the old hypothesis accoring which the He atomic species can be used also to mimick collisions involving non-rotating H2. An accurate investigation on the interaction between CC- and He has also been carried out.