Abstract
The first interferometric measurements have been made of the 2(11)-2(12) K-doublet line of ortho-H2CO for a source near the site of the OH/H2O maser source denoted as DR 21(OH) or W75(S). The precise location of the emission, its extent, and the physical conditions in the region are determined. The emission is consistent with quasi-thermal excitation and displays two peaks with brightness temperatures of 2 K or higher separated by 9 arcsec. The overall convolved FWHP size of the region is 18 arcsec by 6 arcsec or less. Assuming that the doublet emission requires an H2 density of a million per cubic centimeter, the total mass is between 6 and 150 solar masses. The mass in the absorption region is roughly five solar masses.