DETECTION OF [O-I] LAMBDA-6300 EMISSION FROM THE DIFFUSE INTERSTELLAR-MEDIUM

The Wisconsin H alpha Mapper facility was used to obtain spectra of [O I] lambda 6300 in three directions that sample the warm ionized compo nent of the interstellar medium at the Galactic midplane and at z simi lar or equal to -300 pc. Weak interstellar [O I] emission was clearly detected toward all three directions, with [O I] lambda 6300/H alpha i ntensity ratios for individual radial velocity components that range f rom less than 0.01 to approximately 0.04. According to photoionization models of the warm ionized medium, these [O I]/H alpha ratios suggest that most of the H alpha originates from density-bounded, nearly full y ionized regions along the lines of sight rather than from partially ionized H I clouds or layers of H II on the surfaces of H I clouds.