Star formation and ionization in the 3 kiloparsec arm.

New recombination line observations, together with existing data on H II regions and type I OH masers, show that there is little star formation occurring in the numerous molecular clouds of the 3 kpc arm. The total mass of ionized gas in the arm cannot be as large as the mass of neutral material, and may actually be quite small. The recombination line observations give no indication of the postulated far side of the 3 kpc arm. The absence of traces of star formation argues that the 3 kpc arm is not a material feature moving supersonically through the interstellar medium nor is it like the rings of H II regions seen in the interior of some galaxies. The 3 kpc arm does have some of the morphological characteristics of gas in a bar, but there is no evidence that it is a continuous feature around the galactic center.