Formation of the BeH+ and BeD+ Molecules in Be+ + H/D Collisions Through Radiative Association

Cross sections and rate coefficients for the formation of BeH+ and BeD+ molecules in Be+ + H/D collisions through radiative association are calculated using quantum mechanical perturbation theory and Breit-Wigner theory. The local thermodynamic equilibrium limit of the molecule formation is also studied, since the process is also relevant in environments with high-density and/or strong radiation fields. The obtained rate coefficients may facilitate the kinetic modelling of BeH+/BeD+ production in astrochemical environments as well as the corrosion chemistry of thermonuclear fusion reactors.

Formation of Al containing molecular complexes in the gas phase in dense molecular clouds: quantum study of the radiative association of Al++H2 and Al++D2

ABSTRACT Radiative association (RA) of Al+ with H2 is the first step in the formation of AlH in gas phase and is here investigated theoretically. We use recent potential energy and dipole moment surfaces and a quantum approach based on the driven equations formalism for performing the dynamics for both the Al+-H2 and Al+-D2 systems. The obtained RA rate coefficients are compared with previous evaluations based on transition state theory and found to be orders of magnitude larger. They are also compared to those obtained recently for the similar systems Na+-H2/D2. The possible role played by RA of Al+ with H2 in the gas phase chemistry of dense molecular clouds is discussed.

Radiative association for the formation of MgO

ABSTRACT The radiative association process for the formation of magnesium oxide (MgO) may be of great importance due to its frequent occurrence in the low-density and dust-poor astrochemical environments. In this work, the cross-sections and rate coefficients for the A1Π → X1Σ+, ${\rm X}^1\Sigma ^+\, \rightarrow \, {\rm A}^1\Pi$, D1Δ → A1Π, a3Π → e3Σ−, ${\rm X}^1\Sigma ^+\, \rightarrow \, {\rm X}^1\Sigma ^+$, and A1Π → A1Π radiative association processes of forming MgO are theoretically estimated. The cross-sections for the transitions between the different states are obtained by using the semiclassical method for direct contributions and the Breit–Wigner theory as a complement for resonance contributions. For the transitions between the same states, the quantum mechanical method is used. The rate coefficients are then obtained from the cross-sections for the temperatures in the range of 10–10 000 K and the results are found to vary from 4.69 $\times \, 10^{-16}$ to 6.27 $\times \, 10^{-14}$ cm3 s−1. For temperatures lower than around 693 K, the rate coefficients for the A1Π → X1Σ+ process are dominant, which indicates this process is the most efficient way of producing MgO at low temperatures. However, the rate coefficients for the D1Δ → A1Π process go through a rapid increase with increasing temperature and become dominant at higher temperatures. For other processes, their rate coefficients are several orders of magnitude lower than those for the two processes mentioned above. The results can be used to further investigate the formation and evolution of MgO in low density and hot gas close to the photosphere of evolved oxygen-rich stars.

Profiling astrophysically relevant MgC4H chains. An attempt to aid astronomical observations

ABSTRACT In this paper, we report results of an extensive theoretical study on MgC4H chains conducted at DFT and CCSD(T) levels motivated by the recent discovery of this species in IRC+10216. A detailed characterization of both neutral and charged species is presented, which include structural, chemical bonding and vibrational properties, rotational, centrifugal distortion and Watson l-type doubling constants, dipole moments, Fermi contact, and spin-rotation constants. In addition, we present ab initio estimates needed for subsequent astrochemical evolution modelling (e.g. dissociation energies, acidity, electron attachment, and ionization energies and related chemical reactivity indices). Possible formation pathways are also discussed. They comprise exchange, (radiative) association, dissociative recombination, and ion neutralization reactions. As an important result aiming at stimulating further observational searching, we suggest that MgC4H− anions should also be observable via rovibrational spectroscopy. The reason is twofold: (i) Neutral MgC4H0 chains possess a sufficiently large dipole moment consistent with dipole-bound anion states and large electron attachment cross-sections. (ii) MgC4H− anions possess a dipole substantially larger than MgC4H0 neutrals (and also larger than that estimated earlier for the longest astronomically detected C8H− anion). This makes MgC4H− anion intensities in rovibrational spectrum experimentally accessible even in the unlikely case of a relative abundance MgC4H−/MgC4H0 comparable to that of CH4, whose anion has the lowest relative abundance observed so far in space because weakly polar C4H0 chains do not support dipole-bound anion states. A suggestion on why, counterintuitively, the MgC2H abundance found in IRC+10216 was lower than that of the longer MgC4H is also presented.

Formation of CO+ by radiative association II

ABSTRACT Radiative association of an oxygen atom with a carbon cation is investigated using quantal and semiclassical methods. The total rate coefficient for spontaneous radiative association of O(2s22p4, 3P) with C+(2s22p, 2P) on the doublet manifold is determined from the corresponding cross-sections. The cross-sections for the ${\rm 1}^2\, \Sigma ^-\rightarrow {\rm A}^2\Pi$, ${\rm 2}^2\, \Sigma ^-\rightarrow {\rm A}^2\Pi$, and ${\rm C}^2\, \Delta \rightarrow {\rm A}^2\Pi$ continuum-bound processes are calculated either semiclassically, in combination with the Breit–Wigner approach, or fully quantum mechanically. In the temperature range 10–10 000 K, our recommended total rate coefficient, obtained from these calculations and the data of Zámečníková et al. (2019), slowly increases from 7.5 × 10−18 cm3s−1 to 2.1 × 10−17 cm3s−1. Corresponding aspects of the CO+ and CO formations in SN 1987A are discussed.