H I emission-absorption experiments toward Galactic H II regions

21 cm atomic hydrogen emission-absorption experiments have been conducted toward 19 Galactic H II regions lying within 1 deg of the Galactic plane. With the exception of one source, absorption has been detected at the hydrogen recombination line velocity of each H II region. 141 absorption features at positive LSR velocities have been identified. If the observed absorption is solely due to cold gas attenuating thermal continuum, these data can provide kinematic distance estimates for the H II regions. Approximately 40 percent of the absorption features are correlated with (C-13)O emission. Nearly 17 percent of the (C-13)O lines appear not to be associated with H I absorption. The derived spin temperatures for these features range from 25 to about 350 K. The measured optical depths are strongly correlated with the spin temperatures. 14 refs