Dynamics of HeHHe⁺ Rotational State Changes Induced by Collision with He: A Possible New Path in Early Universe Chemistry

Abstract

Ab initio calculations are employed to generate the rigid rotor (RR) potential energy surface (PES) describing the interaction of the linear molecular cation HeHHe + , at its equilibrium geometry, with the neutral He atom. The resulting interaction is employed to investigate the efficiency of rotational state-changing collisions at the temperatures relevant to the early universe conditions, where the latter molecule has been postulated to exist, albeit not yet observed. The inelastic rate coefficients are found to be fairly large and are compared with those found for another important cation just recently observed in the interstellar medium: the HeH + polar molecule. The possibility for this cation to provide new options to energy dissipation routes under early universe conditions after the recombination era is briefly discussed.

Quantum Inelastic Scattering of ArHAr+, HeHHe+, and NeHNe+ with He on New Potential Energy Surfaces

“…Such surface was computed at the CCSD­(T) level of theory and extrapolated at the CBS limit. This surface and the one developed in this work for HeHHe + + He show similar behavior, and the value of global minimums is in excellent agreement (−350.0 cm –1 ) …”

“…Very recently, a PES for the HeHHe + + He was reported . Such surface was computed at the CCSD­(T) level of theory and extrapolated at the CBS limit.…”

“…Figure shows the rate coefficients from the lower rotational states of the triatomic molecules. The rates reported by González-Sanchéz et al for HeHHe + + He are also included in this figure. The agreement between both sets of data is excellent.…”

“…R connects the center of mass of the triatom molecules and He, while θ describes the angular orientations of He. The interatomic bond lengths were taken as the vibrationally averaged values in the ground state of the triatomic complexes, r ArH = 1.5188 Å, r HeH = 0.9249 Å, and r NeH = 1.1564 Å …”

“…The rotational constants used are cm –1 and cm –1 , while for HeHHe + , we used the same rotational constant employed by González-Sánchez et al cm –1 . Only rotational states with even values of j exist due to the symmetry of the linear rotors and the fact that Ar, Ne, and He are bosons.…”