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NH3 -- a pyramidal molecular of C_3v point symmetry group. (see its wikipedia entry)

Basic information

Boiling temperature: -33.34 C
Solidify temperature: -77.7 C
The energy barrier of the N inversion: 24.7 kJ/mol
Dipole moment: 1.46D.
Most observed NH3 lines: (J,K)= (1,1) @ 23.694 GHz, (2,2) @ 23.723GHZ, (3,3) @ 23.870GHz
Interstellar abundance: [NH3][H2] = 10^-7 (small dark clouds) - 10^-5 (dense core of OMC)
Major formation route: NH₄⁺ + e- => NH₃ + H  
Major destructrion routes: NH₃ + H₃⁺ => NH₄⁺ + H₂; NH₃ + HCO⁺ => NH₄⁺+ CO.
 Isotopic species detected in space: NH₃, ¹⁵NH₃, NH₂D, NHD₂, ND₃.
 All observable NH3 lines (MHz) from JPL linelist (w\ E_low < 200 cm^-1 & I (300K) > 10^-10)
(Notes: ortho: K=3n; para: K=!3n; metastable: J=K)

• (<100 GHz): 21134.31718; 21703.35813; 22234.49867; 22688.31044; 22834.18499;
                      23098.82675; 23694.49071; 23722.6332 ; 23870.12918; 24139.41638;
• (<1 THz): 331518.2788 ; 332087.39017; 333205.44683; 572498.19918; 642758.0359 ; 645587.66642;
                 714148.38161; 716053.29442; 786799.13221; 858113.28368; 995491.40726;
• (<2 THz): 1000595.16553; 1168452.41204; 1214853.00157; 1215245.76277; 1311481.54797; 1313000.26368; 1381840.94794;
                  1453229.82836; 1453494.46132; 1662290.59326; 1665295.68439; 1763542.68665; 1763822.99154;
• (<3 THz): 2046825.81066; 2047356.95975; 2119262.96154; 2120751.10436; 2357209.82649; 2357728.25096; 2358565.90646; 2400020.72282; 2400578.66558;
                  2402265.79405; 1808934.49663; 1810379.80966; 1976613.23696; 2405124.34610; 2638335.28727; 2639098.07895; 2710949.96553; 2712649.82063;
                  2948395.20369; 2948668.48833; 2949482.12659; 2950819.51642; 2952637.77164; 2989641.12630; 2991556.93898; 2994793.10530; 2999430.21196;
• (<4 THz): 3300025.10586; 3301890.14579; 3376745.68592; 3966575.02172; 4630797.39372; 4635098.49708
  

Observations

• (Kaifu et al., 1975ApJ...201...98K)
  Facts: They mapped the NH3 (J,K) = (1,1), (2,2), (3,3) lines in the Galactic center part using the NRAO 11-m (36-foot) telescope in a region (l = 358.0 deg ~ 2.3deg) and (b = -2'). Beamwidth is 5.3' at (1,1) line frequency, 256-channel filter bank with bandwidth of 64 MHz and spectral resolution of 250 kHz. The survey sensitivity is: Tsys = 650 K, integration time = 15-35 min.
  Conclusions: They found that the L-V relation is strongly asymmetric and strong NH3 sources are concentrated in the region of 0 deg < l < 2 deg and 0 km/s < Vlsr < 100 km/s.
• (Churchwell et al., 1990A&AS...83..119C)
  Facts: They surveyed the NH3 (J,K) = (1,1), (2,2), (3,3) and H2O maser lines in a sample of 84 UCHII regions using the Effelsburg 100-m telescope. The beamwidth is 40" at (1,1) line frequency, two 256-channel AC with bandwidth of 12.5 MHz each and spectral resolution of 22 kHz (~0.30 km/s). The survey sensitivity is: Tsys = 70 K.
  Conclusions: They determined kinematic distances to all sources and found that the galactic lattitude distribution of the sample agree with that of O-type stars. But they didn't see the galactic spiral arm pattern in the sample.The Tk estimated from NH3 lines may be weakly correlated with IR luminosity and line widths.
• (Bell et al., 1993ApJS...86..211B)
  Facts: They surveyed the entire frequency range (17.57~22.04 GHz) including many NH3 lines toward W51 Main/South complex using the NRAO 43-m (140-foot) telescope. Beamwidth is 1.4', two 256-channel Auto-Correlator spectrometers with a total bandwidth of 140 and a spectral resolution of 312.5 kHz. The survey sensitivity is: TA(rms) = 1-5 mK.
  Conclusions: They detected 224 lines (94 H or He recomb. lines + 11 NH3 lines + 19 other lines + 100 U lines). They found that Carbon chain molecules (eg. CnH, CnN, HCnN) are not strong emitters in this source. They found an increasing trend of NH3 excitation temperature with J and J-K values.
• (Vilas-Boas & Abraham, 2000A&A...355.1115V)
  Facts: They surveyed the NH3 (J,K) = (1,1) line toward 108 southern HII regions in the region (l = 270 deg ~ 15 deg) using the Itapetinga Radio Observatory 13.7-m telescope. Beamwidth is 4' at (1,1) line frequency , 256-channel AOS with bandwidth of 41 MHz and spectral resolution of 70 kHz. The survey sensitivity is: Tsys = 130~220 K, TA*(rms) = 0.05K.
  Conclusions: They found 21 new NH3 sources. Detection ratio of NH3 among these HII regions is 30%, except the (l = 270 deg ~ 290 deg) region where no NH3 where detected. The number of NH3 sources is inversely proportional to column density and GC distance.
• (Nagayama et al., 2007PASJ...59..869N)
  Facts: They mapped the NH3 (J,K) = (1,1), (2,2) lines simultaneously in the major part of the central molecular zone (CMZ) of the Galaxy using the Kagoshima 6m telescope in a region (-1.000 deg < l < 1.625 deg) and (-0.375 deg < b < 0.250 deg). Beamwidth is 9.5', 2048 AOS with bandwidth of 250 MHz and spectral resolution of 250 kHz. The survey sensitivity is 80 mK at 5 km/s resolution.
  Conclusions: They confirmed that the gas component is much warmer (80% w\ Tk = 20~80K; 20% w\ Tk > 80K) than the dust component (20K). They also concluded that the GC has a "core" of warm and dense clouds traced by NH3 and a "envelope" of less dense but hotter clouds around the core. Heating of the hot envelope could be due to ambipolar diffusion and the X-ray emission from hot plasma.
• (Sorai et al., 2008PASJ...60.1285S)
  Facts: They mapped the NH3 (J,K) = (1,1), (2,2), (3,3) lines (3 lines simultaneously) at 42 positions in the molecular cloud complex of  W 51 region using the Tomakomai 11-m radio telescope. Beamwidth is 4.5', 2048-channel spectrometer with bandwidth of 16 MHz (~200 km/s) and spectral resolution of 7.8 kHz (~0.1 km/s) .
  Conclusions: They found a Tex = 40 K in the central part of W51A complex and Tex = 20K in other positions. They also found a weak trend of decreasing ortho/para ratio with increasing Tex, L_IR and SFR efficiency.
• (Pineda et al., 2010arXiv1002.2946P)
  Facts: They mapped the NH3 (J,K) = (1,1), (2,2) line in the B5 region in Perseus using the GBT 100-m telescope in a region ~11'x14'. Beamwidth is 31", 4096-channel spectrometer with bandwidth of 12.5 MHz and spectral resolution of 3.05 kHz (~0.04 km/s) .
  Conclusions: They found that the NH3 emission region is more extended than the continuum emission region of dust. The velocity dispersion is low inside a clude core, whilst it will increase sharply at the edge of the cloud core (~ 3 km/s/pc).