Spectroscopy of Triatomic Hydrogen Molecules in a Beam

The formation of beams of triatomic deuterium D₃ and the mixed isotopic molecule D₂H was optically observed for the first time when the corresponding ions were neutralized by charge exchange. The molecules were detected via the transitions between the Rydberg states n=3 and n=2. An assignment of the D₂H spectrum is given. The total lifetimes of rotational sublevels of different electronic states with n=3 of D₃ were measured from the radiative decay of molecules along their path behind the charge-exchange region. Agreement with theory is satisfactory.