Speaker
Description
Recent astronomical observations [1,2] have shown that chloronium (H$_2$Cl$^+$) is an important intermediate in Cl-chemistry of the interstellar medium (ISM) due to its specific thermodynamic properties. For a proper interpretation of the astronomical observations, radiative transfer modelling is required that takes into account the non-local thermodynamic equilibrium (non-LTE) effects of the environment through reliable collisional rate coefficients, which have been lacking in the literature so far for chloronium.
We have recently calculated the first accurate 5-dimensional interaction potential between H$_2$Cl$^+$ and molecular hydrogen (H$_2$), which allowed their rotational excitation to be studied from accurate quantum scattering theories [3]. State-to-state rotational (de-)excitation cross sections have been calculated using the numerically exact close-coupling (CC) scattering method for collision energies from the first inelastic threshold up to 1500 cm$^{-1}$, involving the lowest 21 rotational states for both the ortho and para nuclear spin species. This allowed the thermal rate coefficients to be derived up to kinetic temperatures of 200 K. Finally, the importance of the collisional rate coefficients is demonstrated by non-LTE radiative transfer modelling of some H$_2$Cl$^+$ rotational transitions that have been observed in different interstellar sources.
[1] D. A. Neufeld et al. Astrophys. J. 2015, 807, 54.
[2] S. H. J. Wallström et al. Astron. Astrophys. 2019, 629, A128.
[3] S. Demes et al. J. Phys. Chem. A 2025, 129, 253.
