10min:

DAMIAN L. KOKKIN, CARL A. GOTTLIEB, 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; AND SANDRA BRÜNKEN, Laboratoire de Chimie Physique Moléculaire, École Polytechnique Fédérale de Lausanne, Station 6, CH-1015 Lausanne, Switzerland.

Until this work, the rotational spectra of the silicon isotopic species of SiCC were based almost entirely on astronomical frequencies, because only the fundamental 1_0,1 - 0_0,0 transition ²⁹SiC₂ and ³⁰SiC₂ had been measured in the laboratory. We have now derived precise rotational and centrifugal distortion constants from laboratory measurements of 35~transitions of each isotopic species between 140 and 360~GHz with J \le 10 and K_a \le 8. The rotational spectra calculated with the laboratory measured constants are about two orders of magnitude more accurate than that of He et al. ,\footnoteJ.~H.~He, Dinh-V-Trung, S.~Kwok, H.~S.~P.~Müller, Y.~Zhang, T.~Hasegawa, T.~C.~Peng, and Y.~C.~Huang, \sl Astrophys. Journ. Suppl. Ser., 177, 275 (2008). who determined the spectroscopic constants from about 20~lines of ²⁹SiC₂ and of ³⁰SiC₂ in the wide-line source IRC+10216. The new laboratory measurements should aid assignment of the silicon isotopic species of SiCC in the spectral line survey of IRC+10216 with the SMA, and in future observations with ALMA.