15min:

FILIPPO TAMASSIA, Dipartimento di Chimica Fisica ed Inorganica, Universitá di Bologna, V.le Risorgimento 4, I-40136 Bologna, Italy; MICHAEL C. MCCARTHY AND PATRICK THADDEUS, Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, and School of Engineering & Applied Sciences, Harvard University, 29 Oxford St., Cambridge, MA 02138.

The rotational spectrum of the free radical SiOH in its X²A' ground electronic state has been observed by Fourier transform microwave spectroscopy. The 1_0,1-0_0,0 transition has been detected for the main species ²⁸Si¹⁶OH and for the rare isotopic species ³⁰Si¹⁶OH, Si¹⁸OH, and SiOD. The same transition has also been observed in the excited vibrational states v₂=1 and v₃=1 for the most abundant species. From this data, precise spectroscopic constants have been derived for this plausible astronomical molecule, as has an experimental structure (r₀).

In addition, the 1_0,1-0_0,0 transition of HNSi has been detected at high spectral resolution by the same technique, yielding a precise value for the nitrogen quadrupole coupling constant.