Context : The initial stage of star formation is a complex area of study because of the high densities ( n _ { H _ { 2 } } > 10 ^ { 6 } cm ^ { -3 } ) and low temperatures ( T _ { dust } < 18 K ) involved .
Under such conditions , many molecules become depleted from the gas phase by freezing out onto dust grains .
However , the deuterated species could remain gaseous under these extreme conditions , which would indicate that they may serve as ideal tracers .

Aims : We investigate the gas dynamics and NH _ { 2 } D chemistry in eight massive precluster and protocluster clumps ( G18.17 , G18.21 , G23.97N , G23.98 , G23.44 , G23.97S , G25.38 , and G25.71 ) .

Methods : We present NH _ { 2 } D 1 _ { 11 } -1 _ { 01 } ( at 85.926 GHz ) , NH _ { 3 } ( 1 , 1 ) , and ( 2 , 2 ) observations in the eight clumps using the PdBI and the VLA , respectively .
We used 3D GAUSSCLUMPS to extract NH _ { 2 } D cores and provide a statistical view of their deuterium chemistry .
We used NH _ { 3 } ( 1 , 1 ) and ( 2 , 2 ) data to investigate the temperature and dynamics of dense and cold objects .

Results : We find that the distribution between deuterium fractionation and kinetic temperature shows a number density peak at around T _ { kin } = 16.1 K and the NH _ { 2 } D cores are mainly located at a temperature range of 13.0 to 22.0 K. The 3.5 mm continuum cores have a kinetic temperature with a median width of 22.1 \pm 4.3 K , which is obviously higher than the temperature in NH _ { 2 } D cores .
We detected seven instances of extremely high deuterium fractionation of 1.0 \leqslant D _ { frac } \leqslant 1.41 .
We find that the NH _ { 2 } D emission does not appear to coincide exactly with either dust continuum or NH _ { 3 } peak positions , but it often surrounds the star-formation active regions .
This suggests that the NH _ { 2 } D has been destroyed by the central young stellar object ( YSO ) due to heating .
The detected NH _ { 2 } D lines are very narrow with a median width of 0.98 \pm 0.02 { km~ { } s } ^ { -1 } , which is dominated by non-thermal broadening .
The extracted NH _ { 2 } D cores are gravitationally bound ( \alpha _ { vir } < 1 ) , they are likely to be prestellar or starless , and can potentially form intermediate-mass or high-mass stars in future .
Using NH _ { 3 } ( 1 , 1 ) as a dynamical tracer , we find evidence of very complicated dynamical movement in all the eight clumps , which can be explained by a combined process with outflow , rotation , convergent flow , collision , large velocity gradient , and rotating toroids .

Conclusions : High deuterium fractionation strongly depends on the temperature condition .
Tracing NH _ { 2 } D is a poor evolutionary indicator of high-mass star formation in evolved stages , but it is a useful tracer in starless and prestellar cores .