Interstellar SiN

We report the detection of the silicon nitride (SiN) $N=2$–1, $J=5/2$–3/2 transition toward SgrB2(M), in absorption. Although it has been seen in a circumstellar envelope before, this is the first time this molecule has been detected in interstellar space. We estimate a column density of $(1-2) \times 10^{13}$ cm-2, which is a factor of 20-50 lower than that of silicon monoxide (SiO) toward this source. It is likely that this molecule, like SiO and FeO, is created by gas-phase chemistry after refractory elements, previously locked up in grain cores, have been released by sputtering in shocks.