Wilson et al. 1971
Wilson, R.W., A.A. Penzias, K.B. Jefferts, M. Kutner, and P. Thaddeus, 1971: Discovery of interstellar silicon monoxide. Astrophys. J., 167, L97-L100, doi:10.1086/180769.
Line emission attributed to the J=3→2 rotational transition of SiO has been detected in Sgr B2, at a radial velocity comparable to that of other molecules; the estimated column number density of SiO is 4×1013 /cm2. The line has not been found in Ori A, IRC+10216, Sgr A, W51, DR21, or NML Cyg.