Cooling of primordial gas plays a crucial role in the birth of the first
structures in our Universe. Due to the low fractional abundance of molecular
species at high redshifts, spontaneous emission rather than collisions
represents the most efficient way to cool the pristine plasma. In the present
work, radiative cooling functions are evaluated for the diatomic species HD,
HD$^+$, HeH$^+$, LiH and LiH$^+$. Cooling functions for the triatomic ions
H$_3^+$ and H$_2$D$^+$ are also considered. Analytic fits as functions of
temperature are provided.Comment: 8 pages, 9 figures, 1 tabl
In this work we present a dynamical study of the H + HeH+ → H2+ + He reaction in a collision energy range from 0.1 meV to 10 eV, suitable to be used in applicative models. The paper extends and complements a recent work [ Phys. Chem. Chem. Phys. 2014, 16, 11662] devoted to the characterization of the reactivity from the ultracold regime up to the three-body dissociation breakup. In particular, the accuracy of the quasi-classical trajectory method below the three-body dissociation threshold has been assessed by a detailed comparison with previous calculations performed with different reaction dynamics methods, whereas the reliability of the results in the high energy range has been checked by a direct comparison with the available experimental data. Integral cross sections for several HeH+ roto-vibrational states have been analyzed and used to understand the extent of quantum effects in the reaction dynamics. By using the quasi-classical trajectory method and quantum mechanical close coupling data, respectively, in the high and low collision energy ranges, we obtain highly accurate thermal rate costants until 15 000 K including all (178) the roto-vibrational bound and quasi-bound states of HeH+. The role of the collision-induced dissociation is also discussed and explicitly calculated for the ground roto-vibrational state of HeH+.
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