2005ApJ...622..390C

We present the first astronomical detection of ²⁸Si¹⁸O maser and thermal emission toward Orion KL by using the laboratory-measured line frequencies of ²⁸Si¹⁸O. The simple model of a ²⁸Si¹⁸O maser condition adopting a line overlap mechanism leads us to confirm a maser action in spite of its lowest relative abundance, i.e., ²⁸Si¹⁶O/²⁸Si¹⁸O∼500. Now the ²⁸Si¹⁸O lines can be used to investigate interstellar physics and chemistry, especially when the optical depths of the spectral lines of the main species are high.