Observation of the Infrared Spectrum of the Triatomic Deuterium Molecular Ion D3+

The infrared vibrational-rotational spectrum of the D₃⁺ isotope of the simplest polyatomic molecule is observed. Eight intervals between 1750 and 1850 cm⁻¹ have been measured to an error of 0.0005 cm⁻¹ or 0.3 ppm (at 70% confidence level). Four have been identified as members of the fundamental degenerate vibrational band. The rest apparently involve unidentified higher vibrational-rotational levels.