Interstellar formaldehyde in southern dark dust clouds.

A catalog of 42 dark dust clouds of high visual opacity has been compiled from a study of the Whiteoak Fields (between declinations -33 and -46 deg) of the Palomar Sky Survey, listing the equatorial and galactic coordinates of the cloud centers, the approximate areas, and estimated opacity classes. Formaldehyde has been detected in 33 clouds by means of the molecule's 6-cm rotational transition. Analysis of the hyperfine structure of the absorption profiles from 27 clouds has been performed. Half the analyzed clouds have a mean excitation temperature of 2.2 K, while a third have a temperature of 1.9 K. From kinematical evidence, it is concluded that most of the dark clouds, the Heeschen cold cloud of neutral hydrogen seen towards the galactic-center region, and the local neutral hydrogen of low velocity dispersion are physically associated. A velocity gradient in a cloud complex lying in the constellation Corona Australis is discussed.