The Spin ofSi29and Mass Ratios of the Stable Si Isotopes

The $J=0\mathrm{}\to 1$ microwave transition of ${\mathrm{Si}}^{29}$ ${\mathrm{D}}_3$F has been examined under high resolution for hyperfine structure due to ${\mathrm{Si}}^{29}$. No hyperfine structure was found, which sets an upper limit of 1×${10}^{-28\mathrm{}}$ ${\mathrm{cm}}^2$ to the quadrupole moment of ${\mathrm{Si}}^{29}$. This is good evidence that the ${\mathrm{Si}}^{29}$ spin is ½. The measurement also allows an accurate determination of mass difference ratios for the Si isotopes.