Astophysics: The Electronic Spectrum of H2O+ and Its Relationships to the Observations Made from Herschel, an ESA Space Observatory

Prior to its discovery in 1973 by Hin Lew and I. Heiber, the electronic spectrum of H₂ O+ had been sought for many years, both at the National Research Council of Canada and elsewhere. Astrophysically, H₂ O+ was expected to be a constituent in comet tails since, according to Whipple, the comet nucleus was most probably composed largely of ices, including H₂O and H₂ O+. Spectroscopy of the species provides complementary information of the physical state of the coma to that obtained from the observations of the parent species. With the resultant invention of John Herschel, a European Space Agency space observatory, the first science highlights became plausible. The Heterodyne Instrument for the Far-Infrared (HIFI), is one of the three instruments on board. The HIFI, was designed to provide very high spectral resolution over the widest possible frequency range.