Molecular Deuterations in Massive Starless Clump Candidates

Deuterated molecules are valuable probes for investigating the evolution and the kinematics in the earliest stages of star formation. In this study, we conduct a comprehensive investigation by performing a single-point survey of 101 starless clump candidates, and carrying out on-the-fly (OTF) observations of 11 selected sources, focusing on deuterated molecular lines using the IRAM 30 m telescope. In the single-point observation, we make 46 detections for DCO+ J = 1-0, 12 for DCN J = 1-0, 51 for DNC J = 1-0, 7 for N2D+ J = 1-0, 20 for DCO+ J = 2-1, and 10 for DCN J = 2-1. The starless clump candidates with deuterated molecule detections exhibit lower median kinetic temperatures and a narrower H2CO (1(0,1)-0(0,0)) median full width at half maximum compared to those without such detections, while simultaneously displaying similar median values of 1.1 mm intensity, mass, and distance. Furthermore, our OTF observations reveal that deuterated molecules predominantly have peaks near the 1.1 mm continuum peaks, with the DCO+ J = 1-0 emission demonstrating higher intensity in the deuterated peak region compared to the DCN and DNC J = 1-0 emissions. Additionally, the majority of emissions from deuterated molecules and 13C isotopologues exhibit peak positions close to those of the 1.1 mm continuum peaks. By analyzing the 20 '' x 20 '' regions with strongest deuterated emissions in the OTF observations, we estimated deuterated abundances of 0.004-0.045, 0.011-0.040, and 0.004-0.038 for D frac(HCN), D frac(HCO+), and D frac(HNC), respectively. The differential detection of deuterated molecular lines in our OTF observations could be attributed to variations in critical densities and formation pathways.