The Radiofrequency Spectrum ofRb85F andRb87F by the Electric Resonance Method

Abstract

The radiofrequency spectrum of the two molecular species ${\mathrm{Rb}}^{85}$F and ${\mathrm{Rb}}^{87}$F was studied by the molecular beam electric resonance method. The electrical quadrupole interaction constant, $\frac{e{q}_{1}{Q}_{1}}{h}$, of Rb in RbF was determined for ${\mathrm{Rb}}^{87}$F in rotational states $J=1$ and $J=2$ for the first few vibrational states, and for ${\mathrm{Rb}}^{85}$F in rotational state $J=1$ for the first few vibrational states. The interaction constants are unusually large for an alkali halide molecule; for the zeroth vibrational state of ${\mathrm{Rb}}^{85}$F, $\frac{e{q}_{1}{Q}_{1}}{h}=\ensuremath{-}70.31\ifmmode\pm\else\textpm\fi{}0.10$ Mc/sec. and for the zeroth vibrational state of ${\mathrm{Rb}}^{87}$F, $\frac{e{q}_{1}{Q}_{1}}{h}=\ensuremath{-}34.00\ifmmode\pm\else\textpm\fi{}0.06$ Mc/sec. The absolute value of the interaction constant decreases about 1.1 percent from one vibrational state to the next higher one; the values of the interaction constants for rotational states $J=1$ and $J=2$ are the same within the limit of error. The ratio of the electric quadrupole moment of ${\mathrm{Rb}}^{85}$ to that of ${\mathrm{Rb}}^{87}$ is +2.07\ifmmode\pm\else\textpm\fi{}0.01. Results are reported on the spin-orbit coupling ${c}_{2}({\mathbf{I}}_{2}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{J})$, between the spin of the fluorine nucleus and the molecular rotational angular momentum. For the zeroth vibrational state of ${\mathrm{Rb}}^{85}$F, $|\frac{{c}_{2}}{h}|=11\ifmmode\pm\else\textpm\fi{}3$ kc/sec. and for the zeroth vibrational state of ${\mathrm{Rb}}^{87}$F, $|\frac{{c}_{2}}{h}|=14\ifmmode\pm\else\textpm\fi{}4$ kc/sec. No variation in $|\frac{{c}_{2}}{h}|$, with vibrational state was observed. Finally, an unpredicted line group was observed in the spectrum at one-half the frequency of one of the line groups in the ${\mathrm{Rb}}^{85}$F spectrum. Possible origins of this line group are discussed, including that of a double quantum transition. The vibrational frequency, ${\ensuremath{\omega}}_{0}$, of ${\mathrm{Rb}}^{85}$F is 340\ifmmode\pm\else\textpm\fi{}68 ${\mathrm{cm}}^{\ensuremath{-}1}$.