The Caltech Submillimeter Observatory has detected triply deuterated ammonia , ND _ { 3 } , through its J _ { K } = 1 _ { 0 } ^ { a } \to 0 _ { 0 } ^ { s } transition near 310 GHz .
Emission is found in the NGC 1333 region , both towards IRAS 4A and a position to the South-East where DCO ^ { + } peaks .
In both cases , the hyperfine ratio indicates that the emission is optically thin .
Column densities of ND _ { 3 } are 3 - 6 \times 10 ^ { 11 } cm ^ { -2 } for T _ { ex } =10 K and twice as high for T _ { ex } =5 K. Using a Monte Carlo radiative transfer code and a model of the structure of the IRAS source with temperature and density gradients , the estimated ND _ { 3 } abundance is 3.2 \times 10 ^ { -12 } if ND _ { 3 } /H _ { 2 } is constant throughout the envelope .
In the more likely case that ND _ { 3 } /H _ { 2 } D ^ { + } is constant , ND _ { 3 } /H _ { 2 } peaks in the cold outer parts of the source at a value of 1.0 \times 10 ^ { -11 } .
To reproduce the observed NH _ { 3 } /ND _ { 3 } abundance ratio of \sim 1000 , grain surface chemistry requires an atomic D/H ratio of \approx 0.15 in the gas phase , > 10 times higher than in recent chemical models .
More likely , the deuteration of NH _ { 3 } occurs by ion-molecule reactions in the gas phase , in which case the data indicate that deuteron transfer reactions are much faster than proton transfers .