Rate coefficients for pure rotational quenching in H 2 (ν 1 = 0, j 1) + H 2 (ν 2 = 0, j 2) collisions from initial levels of j 1 =2-31 (j 2 = 0 or 1) to all lower rotational levels are presented. We carried out extensive quantum mechanical close-coupling calculations based on a recently published H 2-H 2 potential energy surface (PES) developed by Patkowski et al. that has been demonstrated to be more reliable than previous work. Rotational transition cross sections with initial levels of j 1 =2-14, 18, 19, 24, and 25 were computed for energies ranging from 10 −6 to 1000 cm −1 , while the coupled-states approximation was adopted from 2000 to 20,000 cm −1. The corresponding rate coefficients were calculated for the temperature range 10 −5 T10,000 K. Scaling methods based on the ultra-cold data (10 −5-1 K) were used to estimate rate coefficients for all other intermediate rotational states. Comparisons with previous work that adopted different PESs show small discrepancies at high temperatures and in low-energy resonance regions. The astrophysical applications of the current results are briefly discussed, including the rotational H 2 critical densities due to para-H 2 and ortho-H 2 collisions.

Rate coefficients for rotational transitions in HD induced by H2 impact for rotational levels of HD j ≤ 8 and temperatures 10 K ≤ T ≤ 5000 K are reported. The quantum mechanical close-coupling (CC) method and the coupled-states (CS) decoupling approximation are used to obtain the cross-sections employing the most recent highly accurate H2–H2 potential energy surface (PES). Our results are in good agreement with previous calculations for low-lying rotational transitions The cooling efficiency of HD compared with H2 and astrophysical applications are briefly discussed.

No abstract

Fine-structure line emission from [Ne ii] is observed in the infrared (12.81 μm) and could serve as a diagnostic of X-ray irradiation in protoplanetary disks. [Ne ii] emission may also trace the disk gas and indicate the presence of shocks due to outflows. As the electron fraction decreases with decreasing height from the plane of a disk, collisions with atomic hydrogen begin to play an important role in populating excited fine-structure levels. We present computations of cross sections for fine-structure excitation in collisions of with atomic hydrogen using a fully quantal molecular-orbital close-coupling approach with complete angular momentum coupling. The results are based on accurate calculations of NeH+ molecular potentials obtained from the multireference single- and double-excitation configuration interaction method. We find that the excitation cross sections are dominated by resonances at energies below 1000 cm−1. Quenching rate coefficients are given at temperatures (10–2000 K) of astronomical interest and compared with the electron impact rate.

Direct detection of gravitational waves (GWs) on 17 August 2017, propagating from a binary neutron star merger, or a “kilonova”, opened the era of multimessenger astronomy. The ejected material from neutron star mergers, or “kilonova”, is a good candidate for optical and near infrared follow-up observations after the detection of GWs. The kilonova from the ejecta of GW1780817 provided the first evidence for the astrophysical site of the synthesis of heavy nuclei through the rapid neutron capture process or r-process. Since properties of the emission are largely affected by opacities of the ejected material, enhancements in the available r-process data is important for neutron star merger modeling. However, given the complexity of the electronic structure of these heavy elements, considerable efforts are still needed to converge to a reliable set of atomic structure data. The aim of this work is to alleviate this situation for low charge state elements in the Os-like isoelectronic sequence. In this regard, the general-purpose relativistic atomic structure packages (GRASP0 and GRASP2K) were used to obtain energy levels and transition probabilities (E1 and M1). We provide line lists and expansion opacities for a range of r-process elements. We focus here on the Os isoelectronic sequence (Os I, Ir II, Pt III, Au IV, Hg V). The results are benchmarked against existing experimental data and prior calculations, and predictions of emission spectra relevant to kilonovae are provided. Fine-structure (M1) lines in the infrared potentially observable by the James Webb Space Telescope are highlighted.