Direct observation of the fine structure transitions in the Ne+ and Ar+ ions with diode lasers

The 2P1/2–2P3/2 fine structure transitions in the ground (np5) state of the neon (n=2) and argon (n=3) atomic ions have been observed in absorption in the positive column of a liquid–nitrogen cooled discharge cell, by employing tunable infrared diode lasers as sources. The transition frequencies were measured to be 780.4240±0.0011 and 1431.5831±0.0007 cm−1 for Ne+ and Ar+, respectively. A few transitions have also been observed for the neutral Ne and Ar atoms.