Observation of the Infrared Spectrum ofH3+

The infrared ${\nu }_2$ band of ${\mathrm{H}}_3^{+}$ has been observed. A direct infrared absorption method combining a liquid-nitrogen-cooled multiple-reflection discharge cell and a difference-frequency laser system has been used for the detection. Fifteen absorption lines have been measured in the region of 2950-2450 ${\mathrm{cm}}^{-1\mathrm{}}$ and assigned. This is the first spectroscopic detection of this fundamental molecular ion in any spectral range.