The 4830 MHz absorption line of formaldehyde has been observed in the SNR complex W44 and the H ii region complex W3. The results are presented as maps of apparent optical depth. The formaldehyde is concentrated toward the eastern edge of the shell and reaches a maximum apparent optical depth of 1.5 compared with 0.2 for OH; furthermore the centers of the H2CO and OH concentrations are displaced by about 6′. The velocities of the H2CO and OH agree and both molecular lines have the same velocity gradient across the source.
The H2CO absorption profiles for W3 (IC 1795) exhibit at least two narrow components whose average velocity becomes more negative toward the NE. The greatest optical depth occurs where the optical obscurration is high but not at the position of maximum Av. A general agreement between the velocities of other molecules and the H2CO values is indicated.