DETECTION OF SiOH ($X^2A'$) BY FOURIER TRANSFORM MICROWAVE SPECTROSCOPY

Author Institution: Dipartimento di Chimica Fisica ed Inorganica, Universita di Bologna, V.le Risorgimento 4, I-40136 Bologna, Italy; 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 $X^2A'$ 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 $^{28}$Si$^{16}$OH and for the rare isotopic species $^{30}$Si$^{16}$OH, Si$^{18}$OH, and SiOD. The same transition has also been observed in the excited vibrational states $v_2=1$ and $v_3=1$ for the most abundant species. From this data, precise spectroscopic constants have been derived for this plausible astronomical molecule, as has an experimental structure ($r_0$). 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