The rotational spectra of 29SiC2 and 30SiC2

Abstract

The rotational spectra of 29SiC2 and 30SiC2, two silicon isotopic species of the abundant astronomical ring 28SiC2, have been characterized in the millimeter band between 140 and 360GHz in a low pressure discharge through SiH4, C2H2, and Ar. Precise rotational and centrifugal distortion constants have been derived for both species by fitting a standard asymmetric top Hamiltonian to 38 a-type transitions of 29SiC2 and 35 of 30SiC2; the data sets include transitions up to Ka = 8 and at least J = 16. With these new measurements in hand, the most intense radio transitions of both species either have been measured or can now be predicted to better than 1kms -1 in equivalent radial velocity up to 500GHz, more than adequate accuracy for spectral line identifications in circumstellar shells of evolved carbon stars such as IRC+10216 where SiC2 is conspicuous. More than 10 new lines of 29SiC2 and 30SiC2 have been identified between 295 and 354GHz in the interferometric spectral line survey of IRC+10216 with the Submillimeter Array. © 2011. The American Astronomical Society. All rights reserved.