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 360 GHz 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
