Microwave Spectrum of the C3S Molecule in the Vibrationally Excited States of Bending Modes, v4 and v5

Abstract

Rotational spectra of the linear C3S molecule in the excited bending vibrational states ν5 = 1, 2, 3, and 4 (CCS bending) and ν4 = 1 (CCC bending) have been observed in the frequency range 116-383 GHz with a source-modulated microwave spectrometer. Molecular constants of vibration-rotation interaction terms up to higher orders were determined by the least-squares fitting of about 460 transition frequencies. The determined αt, qt, and qJt constants showed a good coincidence with those of ab initio calculation. The sign and magnitude of γll, the dependence of the rotational constant Bv on vibrational angular momentum, was explained by a symmetric-top-like molecular model. The constant qKt, the dependence of the l-type doubling and resonance constant qt on vibrational angular momentum, was determined experimentally for the first time. The obtained value of qKt 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.