Laboratory spectroscopy of H 3 +

The experimental determination of the low–lying rovibrational energy levels of H3+ using high–resolution, high–sensitivity infrared laser spectroscopy has confirmed this ion's equilateral triangle equilibrium geometry, provided direct information on its quantum mechanical characteristics, and enabled its extensive study in planetary ionospheres and in the interstellar medium.Since the discovery of the ν2 ← 0 fundamental band, the laboratory spectroscopy of H3+ has been pushed to higher energies through the study of vibrational hot bands, overtones, forbidden bands and combination bands. We review the 20 years of laboratory spectroscopy of this important ion, discuss our recent work on the ν1 +2ν22 ← 0 and 2ν1 + ν2 ← 0 bands, and examine the prospects for the future of H3+ spectroscopy.