Millimeter-wave spectroscopy of CIBS: An improved evaluation of the equilibrium structure of chlorothioborine

The rotational spectrum of the unstable ClBS molecule has been investigated in the millimeter-wave region, from 80 to 195 GHz. A high-temperature reaction between crystalline boron and disulfur dichloride vapor as used to produce the molecule in a flow pyrolysis system. Eight different isotopic species were studied measuring lines in the ground and excited vibrational states 01(1)0 (ClBS bend). 10(0)0 (Cl-B stretch), 02(0)0, 02(2)0, and 00(0)1 (B=S stretch). The analysis of the spectra has been performed taking simultaneously into account both the Fermi resonance between the 10(0)0 and 02(0)0 states, and l-type resonance effects in the v(2) = 2 vibrational state. This procedure allowed us to calculate directly, deperturbed rotational constants, from which the equilibrium rotational constant of seven isotopic variants could be accurately determined yielding a much improved evaluation of the equilibrium structure of chlorothioborine: r(e)(Cl-B) = 1.6806 +/- 0.0001 Angstrom and r(e)(B=S) = 1.6049 +/- 0.0001 Angstrom. The equilibrium structures of ClBS and of the related molecules HBS, FBS. HCP, FCP, and ClCP have been also theoretically evaluated by high-level CCSD(T) calculations performed using cc-pVTZ. cc-pVQZ. and cc-pV5Z basis sets, The different trends respectively observed for the B=S and C=P bond lengths in the XBS and XCP triatomic molecules are discussed. (C) 2002 Elsevier Science (USA).