Energy-transfer quantum dynamics of HeH+ with He atoms: Rotationally inelastic cross sections and rate coefficients

Abstract

Two different ab initio potential energy surfaces are employed to investigate the efficiency of the rotational excitation channels for the polar molecular ion HeH+ interacting with He atoms. We further use them to investigate the quantum dynamics of both the proton-exchange reaction and the purely rotational inelastic collisions over a broad range of temperatures. In current modeling studies, this cation is considered to be one of the possible cooling sources under early universe conditions after the recombination era and has recently been found to exist in the interstellar medium. The results from the present calculations are able to show the large efficiency of the state-changing channels involving rotational states of this cation. In fact, we find them to be similar in size and behavior to the inelastic and reaction rate coefficients obtained in previous studies, where H atoms were employed as projectiles. The same rotational excitation processes, occurring when free electrons are the collision partners of this cation, are also compared with the present findings. The relative importance of the reactive, proton-exchange channel and the purely inelastic channels is also analyzed and discussed. The rotational de-excitation processes are also investigated for the cooling kinetics of the present cation under cold trap conditions with He as the buffer gas. The implications of the present results for setting up more comprehensive numerical models to describe the chemical evolution networks in different environments are briefly discussed.

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

“…This is an interesting result which suggests that the efficiency of energy uptake via collisions by the present cation could involve a larger range of possible transitions than would be expected from what other ionic systems have shown in our earlier calculations. 40 …”

“…We have also outlined some further possibilities in the Introduction section and will discuss them more specifically in future work. Since neutral He and neutral H atoms can interact with either of the above ionic molecules, we thought it to be of interest to compare the efficiency of the energy transfer processes involving rotational states of both of them when colliding with surrounding hydrogen atoms, especially since data already exist for the case of HeH + in collision with H from the earlier work reported in refs ( 43 ) and ( 40 ).…”

HeH+ Collisions with H2: Rotationally Inelastic Cross Sections and Rate Coefficients from Quantum Dynamics at Interstellar Temperatures

“…Those data clearly show that the lowest three terms of the expansion with an even index for HeH + ···H 2 are all more strongly attractive than the same terms for the HeH + ···He system from ref ( 28 ), thus suggesting that we should expect a more efficient dynamical coupling of the cation rotational states during collisions with H 2 than with He. With the same token, we also see that the three lowest coefficients with an odd index present more marked repulsive potential branches at short-range interactions for HeH + ···H 2 , another factor that can enhance the efficiency of rotational inelastic processes.…”

“…The case of the He partner has been extensively discussed in our earlier work. 28 In the Figure 14 , we present a comparison of the lowest six multipolar radial coefficients for these two systems interacting with the cation.…”

“… Comparison of the lowest six multipolar expansion coefficients generated for the 2D RR-PES for the HeH + ···H 2 system, discussed in this work, and that for the HeH + ···He system, taken from ref ( 28 ). …”