An interstellar line coincident with the P(2,l)transition of hydronium (H3O+)
Abstract
Gas-phase interstellar chemistry is thought to be dominated by ion-molecule reactions. Neutral molecular species abound in the dense interstellar clouds, but only seven molecular ions have been detected. Hydronium (H3O+) is predicted in all ion-molecule reactions1-3 to be an abundant molecular ion, forming OH and H2O by dissociative electron recombination reactions. Here we report the detection, towards the Orion-KL nebula, of a weak emission spectral line coincident in frequency with the P(2,l) rotation-inversion transition of H3O+. Although we cannot be certain that this single-line detection is H3O+, we evaluate this possibility with regard to its observed line parameters and, using theoretical chemical models, derive an Orion fractional abundance for H2O (relative to H2) of 10-5 and 10-6 in thermal and non-thermal cases, respectively. We also report 1-mm-wavelength observations towards Orion which yield new interstellar transitions of CH3OH, 34SO2, H2CS, SO, OCS, SiO and two unidentified lines at 307,313 and 304,374 MHz.
- Publication:
-
Nature
- Pub Date:
- August 1986
- DOI:
- 10.1038/322524a0
- Bibcode:
- 1986Natur.322..524H
- Keywords:
-
- Electron Transitions;
- Hydronium Ions;
- Interstellar Chemistry;
- Line Spectra;
- Electron Recombination;
- Interstellar Gas;
- Molecular Clouds;
- Orion Nebula;
- Thermalization (Energy Absorption);
- Astrophysics