2022ApJ...939..102L

We present a study of the chemistry toward 294 dense cores in 12 molecular clumps, using data obtained from the ALMA Survey of 70 μm dark High-mass clumps in Early Stages. We identified 97 protostellar cores and 197 prestellar core candidates, based on the detection of outflows and molecular transitions of high upper-energy levels (E_u/k > 45 K). The detection rate of the N₂D⁺ emission toward the protostellar cores is 38%, which is higher than 9% for the prestellar cores, indicating that N₂D⁺ does not exclusively trace prestellar cores. The detection rates of the DCO⁺ emission are 35% for the prestellar cores and 49% for the protostellar cores, which are higher than those for N₂D⁺, implying that DCO⁺ appears more frequently than N₂D⁺ in both prestellar and protostellar cores. Both the N₂D⁺ and DCO⁺ abundances appear to decrease from the prestellar to the protostellar stage. The DCN, C₂D, and ¹³CS emission lines are rarely seen in the dense cores of early evolutionary phases. The detection rate of the H₂CO emission toward dense cores is 52%, three times higher than that for CH₃OH (17%). In addition, the H₂CO detection rate, abundance, line intensities, and line widths increase with the core evolutionary status, suggesting that the H₂CO line emission is sensitive to protostellar activity.