Revised values for the nuclear quadrupole moments of ${}^{33}\mathrm{S}$ and ${}^{35}\mathrm{S}$

High-level quantum-chemical calculations are reported for the sulfur electric-field gradients of the CS and SiS molecules. Highly accurate values are obtained in these calculations by using coupled-cluster methods for the treatment of electron correlation together with large atomic-orbital basis sets and by taking into account relativistic effects. The computational results for the sulfur electric-field gradient are used to determine revised values for the ${}^{33}\mathrm{S}$ and ${}^{35}\mathrm{S}$ quadrupole moments, thereby taking advantage of available accurate values for the sulfur quadrupole couplings of CS and SiS from the analysis of rotational spectra. The derived values of $-\mathrm{69.4(4)}$ and 48.3(3) mb for ${}^{33}\mathrm{S}$ and ${}^{35}\mathrm{S}$, respectively, are slightly larger in absolute values than the currently accepted values of $-\mathrm{67.8(13)}$ and 47.1(9) mb and, most importantly, have significantly reduced uncertainties.