MICROWAVE-SPECTRUM OF THE C3S MOLECULE IN THE VIBRATIONALLY EXCITED-STATES OF BENDING MODES, NU(4) AND NU(5)

Rotational spectra of the linear C3S molecule in the excited bending v ibrational states upsilon(5) = 1, 2, 3, and 4 (CCS bending) and upsilo n(4) = 1 (CCC bending) have been observed in the frequency range 116-3 83 GHz with a source-modulated microwave spectrometer. Molecular const ants of vibration-rotation interaction terms up to higher orders were determined by the least-squares fitting of about 460 transition freque ncies. The determined alpha(t), q(t), and q(t)(J) constants showed a g ood coincidence with those of ab initio calculation. The sign and magn itude of gamma(ll), the dependence of the rotational constant B(u)psil on on vibrational angular momentum, was explained by a symmetric-top-l ike molecular model. The constant q(t)(K), the dependence of the l-typ e doubling and resonance constant q(t) on vibrational angular momentum , was determined experimentally for the first time. The obtained value of q(t)(K) was a thousand times greater than the theoretical estimate given by Watson's expression, but the order of magnitude of the exper imental value can be understood by an analogy with a slightly asymmetr ic-top molecule. (C) 1995 Academic Press, Inc.