Microwave spectrum, internal rotation, structure and dipole moment of trifluoromethyl mercaptan, CF 3SH

Abstract

The microwave spectra of CF 3SH and CF 3SD have been studied in the frequency range 12–40 GHz in the ground vibrational state. the spectra are heavily complicated by internal-rotation splittings which have been analysed using an IAM treatment of Valenzuela and Woods. The torsional parameters determined for CF 3SH are s=22.7454(3), F=293,364(15) MHz, ϱ=0.980674(3) and β=0.025472(14); and for CF 3SD, s=41.724(2), F=156,314(65) MHz, ϱ=0.96343(2) and β=0.00651(17). The ground-state torsional splitting for CF 3SH, Δ 0=−3021.1(2) MHz, has been combined with early infrared data for tosionally excited states to obtain V 3=448(4) cm −1. Stark effects in the microwave spectrum are significantly affected by internal rotation enabling the orientation of the dipole moment to be determined. The total dipole moment is found to be 1.52(2) D making an angle of 36.0° with respect to the CS bond direction. The zero-point average structure of CF 3SH has been estimated from isotopic data for CF 3SD and CF 34 3SH plus internal-rotation information. The parameters for an assumed staggered conformation are: r(CF)=1.337(5), r(CS)=1.801(10), r(SH)=1.347(4) Å, ∠ CHS=92.0(1)°, ∠ SCF 1=108.4(8)° and ∠ SCF 2,3=112.9(4)°. The CF 3 top is determined to be asymmetric and titled 3.0° away from the SH bond, in keeping with C s overall symmetry of the molecule but in contrast to the C 3v behaviour of the top indicated by the internal rotation.