Knowledge Bank

The spectrum of a tetrahedral molecule $(XY4)$ with a quadrupolar nucleus at its center will not usually exhibit hyperfine structure from nuclear quadrupole coupling; this is due to the absence of an electric field gradient in such a highly symmetrical molecule. However, when the molecule is in a degenerate vibrational state, this symmetry is reduced to produce an electric field gradient at the nucleus and hence a resultant eqQ. By means of sub-doppler infrared spectroscopy, using tunable microwave modulation sidebands on $CO2$ laser lines, we have measured this vibration-induced eqQ in eighteen vibration-rotation transitions in the $\nu 3$ band of $\mathrm{<mrow\; data-mjx-texclass="ORD">189</mrow>}OSO4(I=3/2)$, and we have calculated, by least squares fit, the scalar and tensor coupling constants, $\chi sv$ and $\chi tv$, to be -4.103(48) MHz and -3.090(59) MHz, respectively. We have also determined the tetrahedral splitting constants in $\mathrm{<mrow\; data-mjx-texclass="ORD">189</mrow>}OSO4$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">192</mrow>}OSO4$, by using a combination of infrared-radiofrequency double resonance and saturation Lamb dip spectroscopy. The ground state constant $(Dt)$ and excited vibrational state constant $(Z3t)$ are listed below: [FIGURE]