1. Introduction  
2. Astronomical observations and analysis  
2.1. Local continuum  
2.2. Template  
2.3. NH₃ ice column densities and abundances  
4. Comparison between astronomical and laboratory data  
4.1. 8-10 μm range  
4.2. The 3 and 6 μm ranges  
4.3. Nitrogen ice inventory  
5. Conclusion