A search for interstellar silicon nitride.

A search for the N = 2 - 1 rotational transition of SiN at 87 GHz has established that the ratios of the abundances of this compound to CN, toward the four sources Orion-KL, IRC +10216, Sagittarius B2, and DR 21(OH), are significantly less than the Si-to-C ratio of 0.1. These ratios suggest that either Si is depleted onto grains where CN is present, or that ion-molecule chemistry does not favor the production of SiN. Si-30S has been detected toward IRC +10216, and a comparison with Si-28S and Si-29S yields terrestrial isotopic abundance ratios for Si.