The effect of CO-H2O collisions in the rotational excitation of cometary CO. (arXiv:2001.09562v1 [astro-ph.EP])

The effect of CO-H2O collisions in the rotational excitation of cometary CO. (arXiv:2001.09562v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Faure_A/0/1/0/all/0/1">A. Faure</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lique_F/0/1/0/all/0/1">F. Lique</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Loreau_J/0/1/0/all/0/1">J. Loreau</a>

We present the first accurate rate coefficients for the rotational excitation
of CO by H2O in the kinetic temperature range 5-100 K. The statistical
adiabatic channel method (SACM) is combined with a high-level rigid-rotor
CO-H2O intermolecular potential surface. Transitions among the first 11
rotational levels of CO and the first 8 rotational levels of both para-H2O and
ortho-H2O are considered. Our rate coefficients are compared to previous data
from the literature and they are also incorporated in a simple non-LTE model of
cometary coma including collision-induced transitions, solar radiative pumping
and radiative decay. We find that the uncertainties in the collision data have
significant influence on the CO population distribution for H2O densities in
the range 10^3-10^8 cm^-3. We also show that the rotational distribution of H2O
plays an important role in CO excitation (owing to correlated energy transfer
in both CO and H2O), while the impact of the ortho-to-para ratio of H2O is
found to be negligible.

We present the first accurate rate coefficients for the rotational excitation
of CO by H2O in the kinetic temperature range 5-100 K. The statistical
adiabatic channel method (SACM) is combined with a high-level rigid-rotor
CO-H2O intermolecular potential surface. Transitions among the first 11
rotational levels of CO and the first 8 rotational levels of both para-H2O and
ortho-H2O are considered. Our rate coefficients are compared to previous data
from the literature and they are also incorporated in a simple non-LTE model of
cometary coma including collision-induced transitions, solar radiative pumping
and radiative decay. We find that the uncertainties in the collision data have
significant influence on the CO population distribution for H2O densities in
the range 10^3-10^8 cm^-3. We also show that the rotational distribution of H2O
plays an important role in CO excitation (owing to correlated energy transfer
in both CO and H2O), while the impact of the ortho-to-para ratio of H2O is
found to be negligible.

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