H⁻photodetachment and radiative attachment for astrophysical applications

Abstract

We combine R-matrix calculations, asymptotic relations, and comparison to available experimental data to construct an H − photodetachment cross section reliable over a large range of photon energies and take into account the series of auto-detaching shape and Feshbach resonances between 10.92 and 14.35 eV. The accuracy of the cross section is controlled by ensuring that it satisfies all known oscillator strength sum rules, including contributions from the resonances and single-photon double-electron photodetachment. From the resulting recommended cross section, spontaneous and stimulated radiative attachment rate coefficients are obtained. Photodetachment rates are also computed for the standard interstellar radiation field, in diffuse and dense interstellar clouds, for blackbody radiation, and for high redshift distortion photons in the recombination epoch. Implications are investigated for these astrophysical radiation fields and epochs.

Cavity-Enhanced Photodetachment of H− as a Means to Produce Energetic Neutral Beams for Plasma Heating

“…A plot of the beam photodetachment rate η as a function of the intracavity power is shown in Figure 5, together with what numerical modelling predicts for three possible offsets of the ion beam with respect to the cavity mode. The experimental results appear quite compatible with the value 3.6 × 10 −21 m 2 of the cross-section most widely reported by theorists [12][13][14] or the most recent experimental value [15] if one admits a medium 250 µm offset. The larger value 4.5 × 10 −21 m 2 , which was found to be the most probable in the 2014 measurement [12] (although with a large ±14% uncertainty) would also be compatible with the observation, assuming a δ = 400 µm offset.…”

Experimental and Theoretical Studies of the Isotope Exchange Reaction

“…Within the floating cell, a few percent of the anions are photodetached by a ∼1kW laser beam at a wavelength of λ=808 nm (a photon energy of hν=1.53 eV, where h is Planck's constant and ν the photon frequency). This energy lies close to the maximum of the photodetachement cross section (McLaughlin et al 2017) and generates ground-level atomic D via…”

Laser-driven production of the antihydrogen molecular ion

“…In order to investigate the production of H − 2 , we evaluate the rates for the relevant formation processes, and for those that compete for anti-atom flux, at temperatures below 1 K. We envisage a scenario in which H atoms are trapped in equilibrium, possibly together with ps, without the presence of positrons. This means that we can ignore interactions of the H − analogue, H + (process 2), a species with a very low production rate [44,45]. Furthermore, we consider that the Hs may be laser excited, and in particular to the metastable 2s state (H(2s)) via a twophoton transition from the ground state.…”