In 1956, M. Cantwell predicted theoretically that the spectrum of vibrations of that ion should be observable in the infrared; and the spectra of the deuterium and common hydrogen isotopologues ( and ) should lie closer to visible light and hence easier to observe.  The first detection of the spectrum of  was made by D. Tolliver and others in 1979, at wavenumbers between 1,700 and 1,900 cm.  In 1982, P. Bernath and T. Amano detected nine infrared lines between 2,164 and 3,158 waves per cm.