Signs of rotationalgfactors

The sign of the rotational $g$ factor of acetylene has been directly measured to be positive with respect to the deuteron moment, thus resolving a disagreement between two earlier reported measurements. Corrections to a calculation of the susceptibility of acetylene which used the wrong sign for $g_J$ have been computed. The signs of the $g$ factors for a number of spherical top molecules, C${\mathrm{F}}_4$, Si${\mathrm{F}}_4$, Ge${\mathrm{F}}_4$, and S${\mathrm{F}}_6$, were also measured to be negative, confirming the results of earlier but less-direct experiments.