The chemical structure of high-mass star nurseries is important for a general understanding of star formation .
Deuteration is a key chemical process in the earliest stages of star formation because its efficiency is sensitive to the environment .
Using the IRAM-30 m telescope at 1.3–4.3 mm wavelengths , we have imaged two parsec-scale high-mass protostellar clumps ( P1 and S ) that show different evolutionary stages but are located in the same giant filamentary infrared dark cloud G28.34+0.06 .
Deep spectral images at subparsec resolution reveal the dust and gas physical structures of both clumps .
We find that ( 1 ) the low- J lines of N _ { 2 } H ^ { + } , HCN , HNC , and HCO ^ { + } isotopologues are subthermally excited ; and ( 2 ) the deuteration of N _ { 2 } H ^ { + } is more efficient than that of HCO ^ { + } , HCN , and HNC by an order of magnitude .
The deuterations of these species are enriched toward the chemically younger clump S compared with P1 , indicating that this process favors the colder and denser environment ( T _ { kin } \sim 14 K , N ( NH _ { 3 } ) \sim 9 \times 10 ^ { 15 } cm ^ { -2 } ) .
In contrast , single deuteration of NH _ { 3 } is insensitive to the environmental difference between P1 and S ; and ( 3 ) single deuteration of CH _ { 3 } OH ( > 10 \% ) is detected toward the location where CO shows a depletion of \sim 10 .
This comparative chemical study between P1 and S links the chemical variations to the environmental differences and shows chemical similarities between the early phases of high- and low-mass star-forming regions .