<i>Q</i> / <i>W</i> -band Observations toward Starless Cores in Orion (QWOSCO). I. Overview, Isotopologues, Isomers, and Complex Organics

Abstract Molecular inventories in starless cores are powerful tools for probing the physical and chemical structures at the earliest stages of star formation. Wide-band spectral scans are invaluable for obtaining a comprehensive view of the chemical composition. In this paper, we present the first results from the project Q / W -band Observations toward Starless Cores in Orion, which uses the Yebes 40 m telescope to survey 23 starless cores in the Orion cloud at the Q (31.0–50.5 GHz) and W (71.1–91.4 GHz) bands with a total bandwidth of 40 GHz. We detect approximately 40 molecular species and derive their column densities, with each species exhibiting a characteristic spread of roughly 1 order of magnitude. The derived isomer and isotopologue column density ratios, including A/E, ortho/para, cyclic/linear, HNC/HCN, 12 C/ 13 C, 14 N/ 15 N, 16 O/ 18 O, 32 S/ 34 S, and D/H, are consistent with expectations for starless environments. Our results, together with the literature, suggest that the complex organic molecules CH 3 OH and CH 3 CHO are both likely ubiquitous in starless cores. The column density ratio of CH 3 CHO with respect to CH 3 OH in starless cores is comparable or lower by a factor of around 25 than those in hot corinos at the protostellar stages if the CH 3 OH column density is directly derived or rescaled from that of 13 CH 3 OH, respectively. Accordingly, we discuss the possible roles of methanol opacity and chemical mechanisms across the starless and protostellar stages.