Spectral Survey of the Star Formation Region DR21OH in the 4-mm Wavelength Range

The results of a spectral survey of the region of massive star formation DR21OH in the 4-mm wavelength range are presented. Sixty-nine molecules and their isotopologues have been detected, ranging from simple diatomic or triatomic species such as SO, SiO and CCH, to complex organic molecules such as CH₃OCHO or CH₃OCH₃. The obtained results qualitatively repeat the results of the survey of the same source at 3 mm. The inventories of molecules found at 3 and 4 mm overlap to a great extent. However, at 4 mm we found a number of species that have no allowed transitions in the 3-mm wavelength range, e.g., DCN, DNC, or SO⁺. The bulk of the molecules detected at 4 mm are those that are common for dense cores, e.g., HC₃N or CH₃CCH, but some of the detected species are typical for hot cores. The latter include complex organic molecules CH₃OCHO, CH₃CH₂OH, CH₃OCH₃, etc. However, the detected emission of these molecules probably arises in a gas heated to 30 K only. Nine molecules, including complex species CH₃C₃N, CH₃CH₂CN, CH₃COCH₃, were found by spectral line stacking. This demonstrates the prospects of the method in the study of molecular clouds.