First quantum study of the rotational excitation of HCN by para-H2O: Convergence of quantum results, influence of the potential energy surface, and approximate rate coefficients of interest for cometary atmospheres.

New H2O–H2O collisional rate coefficients for cometary applications

“…3 of Loreau et al 2018a). This result is in agreement with the convergence procedure adopted for HCN-H 2 O (Dubernet & Quintas-Sánchez 2019): it was argued that the convergence of a single cross-section is of very limited interest because the numerous resonances in cross-sections are washed out by the kinetic Boltzmann average, and further washed out when summing and averaging over the states of the collider in order to obtain the meaningful data which are the state-to-state thermalized rate coefficients. Therefore, the state-to-state thermalized rate coefficients calculations were tested with respect to the convergence of the rotational basis sets using CS calculations for a few transitions at a few energies.…”

“…Therefore, the state-to-state thermalized rate coefficients calculations were tested with respect to the convergence of the rotational basis sets using CS calculations for a few transitions at a few energies. The strong couplings in the interaction region and the depth of the potential energy surface meant that they did not reach a full convergence while increasing the size of the basis sets, and they assumed in the end that the CS results would vary within 20 per cent around the given CS data (educated guess based on observation of the oscillations of the results) (Dubernet & Quintas-Sánchez 2019).…”

“…We recall that the water molecules are asymmetric top molecules whose rotational energy levels are characterized by the rotational C 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society quantum number j i , τ i (=k a − k c ). Identical to our previous publications involving the water molecule (Dubernet & Grosjean 2002;Grosjean, Dubernet & Ceccarelli 2003;Dubernet et al 2006Dubernet et al , 2009Daniel et al 2010;Daniel, Dubernet & Grosjean 2011;Dubernet & Quintas-Sánchez 2019), the H 2 O energy levels and eigenfunctions are obtained by diagonalization of the effective Hamiltonian of Kyrö (1981), compatible with the symmetry of the potential energy surface used in the current work.…”

The Leiden Atomic and Molecular Database (LAMDA): Current Status, Recent Updates, and Future Plans

“…Fourth, collisional data with water as partner are needed to interpret cometary observations. Full quantum data for HCN and CO have just appeared [180,181] and more work is underway. The difficulty with molecule-H 2 O collisions is twofold: first, the potential well is much deeper than in molecule-H 2 systems and, second, H 2 O has a denser rotational spectrum than H 2 .…”

“…This means that full close-coupling calculations are prohibitively expensive due to the excessively large number of angular couplings. As a result, the data of [180] were obtained using partially converged coupled-states calculations while those of [181] were computed within the SACM approximation. These two pioneering studies have shown, however, that propensity rules are less pronounced than in molecule-H 2 collisions and that pair correlations and resonant energy transfer between the target and H 2 O play a critical role.…”