The Interaction of Hydrogen with Iron Benzene-1,3,5-Tricarboxylate (Fe-BTC)

Inelastic neutron scattering (INS) spectroscopy is used to explore the 0–12,000 cm−1 range to characterise the interaction of H2 with iron benzene-1,3,5-tricarboxylate (Fe-BTC). Two peaks are observed in the low energy (<350 cm−1) region after exposure to H2. Measurements with hydrogen deuteride (HD) confirm that the peaks originate from H2. The most likely explanation is that there are two populations of H2 (HD) present. For both the H2- and the HD-loaded samples, the higher energy peak is close in energy to that of the pure isotopomer, so it is assigned to bulk-like H2/HD held in pores of the Fe-BTC. The lower energy peak is assigned to H2/HD interacting directly with the Fe ion exposed on dehydration. It was also possible to detect the H–H stretch in the same experiment; however, unfortunately, the instrumental resolution is insufficient to separate the stretch modes of the bound H2 (HD) and that in the pores.

Mass constraints for 15 protoplanetary discs from HD 1–0

Context. Hydrogen deuteride (HD) rotational line emission can provide reliable protoplanetary disc gas mass measurements, but this molecule is difficult to observe and detections have been limited to three T Tauri discs. No new data have been available since the Herschel Space Observatory mission ended in 2013. Aims. We set out to obtain new disc gas mass constraints by analysing upper limits on HD 1–0 emission in Herschel/PACS archival data from the DIGIT key programme. Methods. With a focus on the Herbig Ae/Be discs, whose stars are more luminous than T Tauris, we determined upper limits for HD in data previously analysed for its line detections. We studied the significance of these limits with a grid of models run with the DALI physical-chemical code, customised to include deuterium chemistry. Results. Nearly all the discs are constrained to Mgas ≤ 0.1 M⊙, ruling out global gravitational instability. A strong constraint is obtained for the HD 163296 disc mass, Mgas ≤ 0.067 M⊙, implying Δg/d ≤ 100. This HD-based mass limit is towards the low end of CO-based mass estimates for the disc, highlighting the large uncertainty in using only CO and suggesting that gas-phase CO depletion in HD 163296 is at most a factor of a few. The Mgas limits for HD 163296 and HD 100546, both bright discs with massive candidate protoplanetary systems, suggest disc-to-planet mass conversion efficiencies of Mp/(Mgas + Mp) ≈ 10–40% for present-day values. Near-future observations with SOFIA/HIRMES will be able to detect HD in the brightest Herbig Ae/Be discs within 150 pc with ≈ 10 h integration time.

HD/H2 ratio in the diffuse interstellar medium

ABSTRACT We present a semi-analytical description of the relative hydrogen deuteride (HD)/H2 abundance in the diffuse interstellar medium. We found three asymptotics of the relative HD/H2 abundance for different parts of the medium and their dependence on the physical parameters, namely, number density, intensity of the ultraviolet field, cosmic ray ionization rate, and metallicity. Our calculations are in a good agreement with the full network calculations using Meudon PDR code. We found that in the case of low metallicity and/or higher cosmic ray ionization rate, HD formation rate is significantly enhanced, HD/H2 ratio increases, and the D i/HD transition occurs at lower penetration depth of ultraviolet radiation than the H i/H2 transition. This can explain the observed difference in the HD/H2 abundance between the local and high-redshift measurements.