Dissociative electron attachment to NaCN is investigated theoretically by combining electron scattering calculations, structure calculations and wave packet dynamics. Non-adiabatic couplings between resonant states and electronically bound states of NaCN⁻ are considered. The calculated cross section has a threshold of 0.68 eV. Due to the very narrow autoionization widths of the electronic resonant states, the magnitude of the cross section is very low. Hence, dissociative electron attachment is not a pathway for forming CN⁻ in interstellar space.

Radiation pressure from Lyman-α (Lyα) scattering is a potentially dominant form of early stellar feedback, capable of injecting up to ∼ 100 × more momentum into the interstellar medium (ISM) than ultraviolet continuum radiation pressure and stellar winds. Lyα feedback is particularly strong in dust-poor environments and is thus especially important during the formation of the first stars and galaxies. As upcoming galaxy formation simulations incorporate Lyα feedback, it is crucial to consider processes that can limit it to avoid placing Lambda-cold dark matter in apparent tension with recent JWST observations indicating efficient star formation at Cosmic Dawn. We study Lyα feedback using a novel analytical Lyα radiative transfer solution that includes the effects of continuum absorption, gas velocity gradients, Lyα destruction (e.g. by 2p → 2s transitions), ISM turbulence, and atomic recoil. We verify our solution for uniform clouds using extensive Monte Carlo radiative transfer (MCRT) tests, and resolve a previous discrepancy between analytical and MCRT predictions. We then study the sensitivity of Lyα feedback to the aforementioned effects. While these can dampen Lyα feedback by a factor ≤ few × 10, we find it remains ≥ 5 − 100 × stronger than direct radiation pressure and therefore cannot be neglected. We provide an accurate fit for the Lyα force multiplier MF, suitable for implementation in subgrid models for galaxy formation simulations. Our findings highlight the critical role of Lyα feedback in regulating star formation at Cosmic Dawn, and underscore the necessity of incorporating it into simulations to accurately model early galaxy evolution.

Motivated by the need to model the plasma at ITER, the cross section - both total and differential - and branching ratios for mutual neutralization in collisions of B+ with H- are calculated using a close coupling approach. Potential energy curves and non-adiabatic coupling elements of seven electronic states of BH in 1Σ+ symmetry are computed using the multireference configuration interaction method.

Context. Mutual neutralization (MN) between cations and anions plays an important role in determining the charge balance in certain astrophysical environments. However, empirical data for such reactions involving complex molecular species have been lacking due to challenges in performing experimental studies, leaving the astronomical community to rely on decades-old models with large uncertainties for describing these processes in the interstellar medium.Aims. Our aim is to investigate the MN reaction C60+ + C60− → C60* + C60 for collisions at interstellar-like conditions.Methods. We studied the MN reaction between C60+ and C60− at collision energies of 100 meV using the Double ElectroStatic Ion Ring ExpEriment (DESIREE) and its merged beam capabilities. To aid in the interpretation of the experimental results, semiclassical modeling based on the Landau-Zener approach was performed for the studied reaction.Results. We experimentally identified a narrow range of kinetic energies for the neutral reaction products. Modeling was used to calculate the quantum state-selective reaction probabilities, absolute cross sections, and rate coefficients of these MN reactions, using the experimental results as a benchmark. We compared the MN cross sections with model results for electron attachment to C60 and electron recombination with C60+.Conclusions. Our results show that it is crucial to take mutual polarization effects, the finite sizes, and the final quantum states of both molecular ions into account in order to obtain reliable predictions of MN rates expected to strongly influence the charge balance and chemistry in environments such as dense molecular clouds.

We have developed a method for which a variety of reactive scattering processes involving the H₂ reaction complex can be studied using the same set of potential curves and couplings. The method is based on a close coupling approach in a strict diabatic representation. By rigorously incorporating non-adiabatic couplings among bound states, we enable the computation of final state distributions. Loss into the ionization continuum is accounted for with a non-local complex potential matrix. The method has successfully been applied in the studies of H⁺ + H^- mutual neutralization and H(1s) + H(ns) associative ionization. In this paper, we investigate the applicability of this method to dissociative recombination and resonant ion-pair formation in electron collisions with HD⁺. The importance of a non-local description of autoionization is demonstrated. Calculated cross sections and final state distributions are compared with results from experiments and previous theoretical studies.

We have experimentally studied dissociative recombination (DR) of electronically and vibrationally relaxed ArH⁺ in its lowest rotational levels, using an electron-ion merged-beams setup at the Cryogenic Storage Ring. We report measurements for the merged-beams rate coefficient of ArH⁺ and compare it to published experimental and theoretical results. In addition, by measuring the kinetic energy released to the DR fragments, we have determined the internal state of the DR products after dissociation. At low collision energies, we find that the atomic products are in their respective ground states, which are only accessible via nonadiabatic couplings to neutral Rydberg states. Published theoretical results for ArH⁺ have not included this DR pathway. From our measurements, we have also derived a kinetic temperature rate coefficient for use in astrochemical models.

The mutual neutralization reaction in collisions of Li⁺ with CN⁻ is a promising candidate for rigorous multi-dimensional ab initio studies of atom-molecule charge transfer processes. The reaction is driven by the non-adiabatic interaction between the lowest two ¹A′ electronic states at large Li–CN distances, resulting in a large cross section for mutual neutralization. As a first step, the relevant adiabatic potential energy surfaces and non-adiabatic interaction are computed ab initio, and the process is studied quantum mechanically using the vibrational sudden approximation, where the vibrational and rotational motions of the CN molecule are assumed to be frozen during the collision.

The total and differential cross-sections and final state distribution for mutual neutralization in collisions of Li⁺ with O⁻ were calculated using an ab initio quantum mechanical approach based on potential energy curves and non-adiabatic coupling elements computed with the multi-reference configuration interaction method. The final state distributions favored channels with excited oxygen states, indicating a strong effect of electron correlation, and the electron transfer could not be described by a simple one-electron exchange process.

The problem of asymptotic non-adiabatic couplings in heavy particle collisions is treated using the reprojection method. The mixing matrix that mixes the asymptotic solutions of the coupled states to obtain appropriate boundary conditions is here derived to second order, yielding a faster convergence of the cross section. In addition, the reprojection method is implemented in a diabatic representation and applied to inelastic scattering of Li + Na and H + H collisions and to mutual neutralization in H⁺ + H⁻ collisions.

Associative ionization in collisions of H+ + H- as well as H(1s) + H(ns) with n = 2, 3, 4 is studied theoretically. Relevant adiabatic potential curves and nonadiabatic couplings are calculated ab initio and the autoionization from the lowest electronic resonant states in the 11+g/u and 31+g/u symmetries are considered. The cross sections are obtained by solving the coupled Schrodinger equation, including a complex potential matrix, in a strict diabatic representation. The importance of using a nonlocal description of autoionization is investigated. Associative ionization is also studied for different isotopes of hydrogen. Calculated cross sections are compared with results from measurements.