Identification of hydronium ion (H3O+) in the
interstellar medium involved several reports over half a decade. In 1986,
Wooten et al. and
Hollis et al.
each reported the P(2,1) rotation-inversion transition line in three objects,
OMC-1,
Sgr B2, and
Orion KL.
Confirming lines were subsequently identified in 1991 by
Wooten et al. and
Goicoechea & Cernicharo.
It has also been observed in comets, including
Halley and
Borrelly, as reported by
Balsiger et al. and by
Nordholt et al., respectively.
Hydronium ion (H3O+) is protonated water. It has a
pyramidal structure and is therefore analogous to ammonia (NH3).
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