Collisions between Ca cations and Rb atoms are computed within a quantum approach that generates the most relevant potential energy curves from accurate ab initio methods and carries out the low-energy scattering calculations by including nonadiabatic and spin-orbit coupling terms. The cross sections are obtained at relative energies typical for the likely arrangements of Rb atoms in a Magneto-Optical Trap overlapped with a Coulomb Crystal of Ca cations. The dominant nonadiabatic process is clearly identified and the efficiency of the nonadiabatic coupling terms which lead to the charge-exchange process is discussed.

Aims. We reassess the role of HeH + with the aid of newly calculated rates that use entirely ab initio methods, which thereby allow us to compute with higher accuracy the relevant abundances within the global chemical network of the early universe. A comparison with the similar role of the ionic molecule LiH + is also presented. Methods. Quantum calculations were carried out for the gas-phase reaction of HeH + with H atoms using our new in-house code, based on the negative imaginary potential method. Integral cross-sections and reactive rate coefficients obtained under the general conditions of early universe chemistry are presented and discussed. Results. Using the new reaction rate, the abundance of HeH + in the early universe is found to be more than one order of magnitude higher than in previous studies. Our more accurate findings increase our confidence in detecting cosmological signatures of HeH + .

The relative efficiencies of the chemical pathways that can lead to the destruction of LiH and LiH + molecules, conjectured to be present in the primordial gas and to control molecular cooling processes in the gravitational collapse of the post-recombination era, are revisited by using accurate quantum calculations for the several reactions involved. The new rates are employed to survey the behavior of the relative abundance of these molecules at redshifts of interest for early universe conditions. We find significant differences with respect to previous calculations, the present ones yielding LIH abundances higher than LiH + at all redshifts.

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