Radio Recombination Lines from Diffuse Interstellar Gas

Observations at three galactic longitudes close to the galactic plane and free from H ii regions of high surface brightness show H157a (X18 cm) lines having peak antenna temperatures of 0.050 K and velocity extents as large as 130 km Sri. Assumptions about the thermal fraction of the galactic background radiation permit us to place constraints on the kinetic temperature, emission measure, and electron density of the ionized medium. These spectra are compared with those from neutral atomic hydrogen (X21 cin), and some initial comments are made about the dynamics and distribution of this medium.