Astrophysically motivated laboratory measurements of deuterium reacting with isotopologues of H

Abstract

AbstractH2D+and D2H+are important chemical tracers of prestellar cores due to their pure rotational spectra that can be excited at the ~20 K temperature of these environments. The use of these molecules as probes of prestellar cores requires understanding the chemistry that forms and destroys these molecules. Of the eight key reactions that have been identified (Albertssonet al. 2013), five are thought to be well understood. The remaining three are the isotope exchange reactions of atomic D with H$${ + \over 3}$$, H2D+, and D2H+. Semi-classical results differ from the classical Langevin calculations by an order of magnitude (Moyanoet al.2004). To resolve this discrepancy, we have carried out laboratory measurements for these three reactions. Absolute cross sections were measured using a dual-source, merged fast-beams apparatus for relative collision energies between ~10 meV to ~10 eV (Hillenbrandet al.2019). A semi-empirical model was developed incorporating high level quantum mechanicalab initiocalculations for the zero-point-energy-corrected potential energy barrier in order to generate thermal rate coefficients for astrochemical models. Based on our studies, we find that these three reactions proceed too slowly at prestellar core temperatures to play a significant role in the deuteration of H$${ + \over 3}$$isotopologues.