2000ApJ...535..227S

The 1^a₁₁-1^s₀₁ transition of NH₂D at 110.1536 GHz was surveyed toward 16 cores of high ammonia abundance in 14 cold dark clouds and was detected toward eight cloud cores, L1448, B1, L1489N, L1551N, L1641N, L134N(S), ρ Oph E, and L63, where L134N and L63 are not associated with infrared sources. The column densities of NH₂D were compared with those of the main species NH₃, previously determined for the corresponding sources, and the relative abundance, [NH₂D]/[NH₃], was found to be large, 0.025-0.18, which is among the highest deuterium fractionation so far observed. The relative abundance is remarkably larger than a predicted value by the latest gas-phase chemical model for dark clouds by Howe & Millar. The spectral line of NH₂D was not detected in other dark cloud cores. These results suggest that a part of NH₃ in dark clouds could originate from dust related reactions associated with energetic events.