Collisional energy transfer in the HeH+–H reactive system

Abstract

The HeH+ molecule is the first to be formed in the Universe. Its recent detection, in the interstellar medium, has increased the interest in the study of the physical and chemical properties of this ion. Here, we report exact quantum time-independent calculations of the collisional cross sections and rate coefficients for the rotational excitation of HeH+ by H. Reactive and exchange channels are taken into account in the scattering calculations. Cross sections are computed for energies of up to 10 000 cm−1, enabling the computation of rate coefficients for temperatures of up to 500 K. The strongest collision-induced rotational HeH+ transitions are those with Δj = 1. Previous results obtained using approximate treatment are compared to the new ones, and significant differences are found. The new rate coefficients are also compared to those for electron-impact rotational excitation, and we found that collisions with H dominate the excitation of HeH+ in media where the electron fraction is less than 10−4. In the light of those results, we recommend the use of the new HeH+–H collisional data in order to accurately model HeH+ excitation in both the interstellar media and early Universe.

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

“…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 ).…”

HD–H+ collisions: statistical and quantum state-to-state studies

“…Hence, since the Hamiltonian is symmetric with respect to interchange of the two hydrogens, there will be no coupling between odd (ortho) and even (para) rotational states of H 2 , so that the number of coupled channels is reduced. We then obtained inelastic, reactive and exchange integral cross sections following the approach described by Tao and Alexander 43 and recently used to study the rotational excitation of several hydrides in collision with H [44][45][46][47] . Excited vibrational states up to v = 17 and up to j = 6 (E max = 4.4 eV) are included in the basis to ensure convergence of the cross sections.…”

The Leiden Atomic and Molecular Database (LAMDA): Current Status, Recent Updates, and Future Plans

“…The first type of planned updates are species which the database currently does not cover at all. This category includes the fine structure lines of S-He [106] and Si-He [106]; the noble gas species ArH + -H [107], ArH + -e [108], and HeH + -H [109]; the diatomic ions SH + -e [76] and CH + -He [110,111]; the neutral diatomics H 2 -H [112], NH-He [113], PN-He [114], and PO-He [115]; the triaomics NH 2 -H 2 [116] and C 3 -He [117]; and the 'large' species HOCO + -He [118], and CH 3 OCHO-He [119,120]. We also regard SiS-H 2 [121] in this category, as its rates were obtained by scaling SiO data.…”

“…• HeH + which is a key species in the chemistry of the early Universe [172] and recently detected in a planetary nebula [173,174]. Collisional data with electrons and H atoms exist [108,109], but data with H 2 are still missing, although the HeH + zone contains little H 2 .…”