Rotational spectra of the linear (\mathrm{C}{3} \mathrm{~S}) molecule in the excited bending vibrational states (v{5}=1), 2.3, and 4 (CCS bending) and (v_{4}=1) (CCC bending) have been observed in the frequency range (116-383 \mathrm{GHz}) with a source-modulated microwave spectrometer. Molecular constants of vibrationrotation interaction terms up to higher orders were determined by the least-squares fitting of about 460 transition frequencies. The determined (\alpha_{t}, q_{t}), and (q_{1}^{J}) constants showed a good coincidence with those of ab initio calculation. The sign and magnitude of (\gamma_{l l}), the dependence of the rotational constant (B_{\mathrm{v}}) on vibrational angular momentum, was explained by a symmetric-top-like molecular model. The constant (q_{t}^{K}), the dependence of the (l)-type doubling and resonance constant (q_{t}) on vibrational angular momentum, was determined experimentally for the first time. The obtained value of (q_{i}^{K}) was a thousand times greater than the theoretical estimate given by Watson's expression, but the order of magnitude of the experimental value can be understood by an analogy with a slightly asymmetric-top molecule. (1995 Academic Press. Inc.