Electron driven reactive processes involving H$^+_2$ and HD$^+$ molecular cations in the Early Universe (original) (raw)
Related papers
2017
The processes as: dissociative recombination, dissociative excitation and inelastic or super-elastic collision of molecular cations with electrons are major elementary process in the kinetics and in the energy balance of astrophysically-relevant ionized media (interstellar molecular clouds, planetary atmospheres, early Universe), in edge fusion and in many other cold media. In this work the main interactions and mechanisms governing these processes, successfully modelled by the Multichannel Quantum Defect Theory (MQDT) are presented. Using a stepwise method based on this theory, cross sections and rate coefficients have been obtained for reactions induced on H 2 + , BeH + and BF + .
Formation of hydrogen in the early universe: quasi-molecular mechanism of recombination
Monthly Notices of the Royal Astronomical Society, 2019
The recombination of an electron and a proton is assumed to occur in the presence of another proton, which participates in the process. The system of colliding particles is considered as a quasi-molecule temporarily formed during a collision. This model is employed to treat the formation of atomic hydrogen in the pre-recombination period of evolution of the early universe. According to a quasi-molecular mechanism of recombination, two processes are responsible for the formation of hydrogen in the early universe – a radiative transition of an electron to an excited repulsive state of mathrmH2+\mathrm{ H}_2^ + mathrmH2+ with a subsequent dissociation into a hydrogen atom and a proton, and a radiative transition of an electron to an excited attractive state of mathrmH2+\mathrm{ H}_2^ + mathrmH2+ with a subsequent cascade downward to a low-lying repulsive state. The participation of the nearest neighbouring proton in the process is shown to decrease the probability of recombination on an isolated proton.
Electron-impact processes involving small molecular ions relevant for the astrochemistry
Contributions of the Astronomical Observatory Skalnaté Pleso, 2022
We investigated the electron-impact processes involving hydrogen, lithium and sodium molecular cations. Rate coefficients for the dissociative recombination in domains of principal quantum numbers n ≥ 4 and temperatures from 500 K to 10 000K are reported. Considered collisional processes have an impact on the ionization level and atom excited-state populations as well on optical characteristics. The data are useful for the modeling of the kinetics of the Early Universe and for geocosmical plasma investigation.
Insights Into Chemical Reactions at the Beginning of the Universe: From HeH+ to H3 +
Frontiers in Chemistry, 2021
At the dawn of the Universe, the ions of the light elements produced in the Big Bang nucleosynthesis recombined with each other. In our present study, we have tried to mimic the conditions in the early Universe to show how the recombination process would have led to the formation of the first ever formed diatomic species of the Universe: HeH+, as well as the subsequent processes that would have led to the formation of the simplest triatomic species: H3 +. We have also studied some special cases: higher positive charge with fewer number of hydrogen atoms in a dense atmosphere, and the formation of unusual and interesting linear, dicationic He chains beginning from light elements He and H in a positively charged atmosphere. For all the simulations, the ab initio nanoreactor (AINR) dynamics method has been employed.
The Astrophysical Journal Supplement Series, 2012
Energy exchange processes play a crucial role in the early Universe, affecting the thermal balance and the dynamical evolution of the primordial gas. In the present work we focus on the consequences of a non-thermal distribution of the level populations of H 2 : first, we determine the excitation temperatures of vibrational transitions and the non-equilibrium heat transfer; second, we compare the modifications to chemical reaction rate coefficients with respect to the values obtained assuming local thermodynamic equilibrium; third, we compute the spectral distortions to the cosmic background radiation generated by the formation of H 2 in vibrationally excited levels. We conclude that non-equilibrium processes cannot be ignored in cosmological simulations of the evolution of baryons, although their observational signatures remain below current limits of detection. New fits to the equilibrium and non-equilibrium heat transfer functions are provided.
Journal of Chemical Physics, 2020
We report a large set of state-to-state rate constants for the H + HD reactive collision, using Quasi-Classical Trajectory (QCT) simulations on the accurate H 3 global potential energy surface of Mielke et al. [J. Chem. Phys. 116, 4142 (2002)]. High relative collision energies (up to ≈56 000 K) and high rovibrational levels of HD (up to ≈50 000 K), relevant to various non thermal equilibrium astrophysical media, are considered. We have validated the accuracy of our QCT calculations with a new efficient adaptation of the Multi Configuration Time Dependent Hartree (MCTDH) method to compute the reaction probability of a specific reactive channel. Our study has revealed that the high temperature regime favors the production of H 2 in its highly rovibrationnally excited states, which can de-excite radiatively (cooling the gas) or collisionally (heating the gas). Those new state-to-state QCT reaction rate constants represent a significant improvement in our understanding of the possible mechanisms leading to the destruction of HD by its collision with a H atom.
2021
In our recent papers (Kereslidze et all 2019a, 2021) a non-standard quasi-molecular mechanism was suggested and applied to treat the cosmological recombination. It was assumed that in the prerecombination stage of evolution of the Universe an electron combined with two neighbouring protons and created the hydrogen molecular ion, 2 H + in highly excited states, which then descended into the lower-lying states or dissociated. In this work, we elaborate the scheme of calculation for free-bound radiative transitions into attractive states of 2 H + as functions of redshift z . Together with the earlier developed treatment of bound-bound radiative transitions in 2 H + , the elaborated scheme of calculation can be used for the design of a fast and complete cosmological recombination code.
Monthly Notices of the Royal Astronomical Society, 2020
In the framework of a quasi-molecular approach, the formation of hydrogen atom in the pre-recombination period of evolution of the Universe is analysed quantitatively. Calculations in an adiabatic multilevel representation enable estimates of probabilities of radiative transitions. The quasi-molecular mechanism of recombination allows the formation of hydrogen molecular ion, mathrmH_2+{\mathrm{ H}_2}^+mathrmH_2+, in its ground state. The probability of this process is comparable with the probability of the creation of atomic hydrogen. The participation of a second proton in the recombination increases the binding energy of an electron and decreases the rate of recombination of hydrogen.
Collisional excitation of HD by H
Monthly Notices of the Royal Astronomical Society
The HD molecule plays an important role in many astrophysical environments. Accurate modelling of the gas cooling induced by HD and its abundance in such media requires a proper modelling of its excitation by both radiative and collisional processes. Reliable state-to-state collisional rate coefficients in extended temperature regimes are then essential to allow for the description of different astrophysical environments where deviations from local thermodynamic equilibrium regime can occur. Here, we report exact quantum time-independent reactive scattering calculations for the rovibrational excitation of HD by H. Rate coefficients are computed for temperatures up to 5000 K and transitions between all rovibrational states with internal energies up to 14 000 cm−1. Previous results neglecting reactive and exchange channels of the colliding system are compared to the new ones and significant differences are found. The present work represent a big step in the complete description of the...
AIP Advances, 2012
The Diep and Johnson (DJ) H 2 -H 2 potential energy surface (PES) obtained from the first principles [P. Diep, K. Johnson, J. Chem. Phys. 113, 3480 (2000); 114, 222 (2000)], has been adjusted through appropriate rotation of the three-dimensional coordinate system and applied to low-temperature (T < 300 K) HD+o-/p-H 2 collisions of astrophysical interest. A non-reactive quantum mechanical close-coupling method is used to carry out the computation for the total rotational state-to-state cross sections σ j1j2→j ′ 1 j ′ 2 (ǫ) and corresponding thermal rate coefficients k j1j2→j ′ 1 j ′ 2 (T ). A rather satisfactory agreement has been obtained between our results computed with the modified DJ PES and with the newer H 4