On the basis of (R)CCSD(T) calculations with the cc-pVQZ basis set, accurate equilibrium bond lengths (ca. 0.0005 angstrom accuracy) are established for linear carbon chains of type SiCnO with n = 3-8. SiC and CO equilibrium bond lengths are in the range 1.683-1.735 and 1.165-1.167 angstrom, respectively. A narrow range (1.272-1.287 angstrom) is obtained for all 25 carbon-carbon equilibrium distances. The equilibrium dipole moments (mu(e)) exhibit large correlation effects. The mu(e) values for the closed-shell species with even integer n are larger than those for the triplet ground states of SiCnO chains with odd n values. Various spectroscopic constants such as harmonic vibrational wavenumbers, vibration -rotation coupling, and 1-type doubling constants are calculated. The ground-state rotational constants of SiC3O, SiC4O, and SiC5O are predicted with ca. 0.1% accuracy to be 1386.5, 867.0, and 564.4 MHz.