Radiofrequency Spectra ofLi6F19by the Molecular Beam Electric Resonance Method

The electric resonance method of molecular beam spectroscopy has been used to study the rotational Stark transitions $J$, $m_J\to J$, $m_{J^{\prime }}$ for ${\mathrm{Li}}^6$ ${\mathrm{F}}^{19}$. A new type of homogeneous electric field of high resolution was used to observe the transitions. A mass spectrometer was used to separate the ${\mathrm{Li}}^6$ (8 percent abundant) and ${\mathrm{Li}}^7$ (92 percent abundant) positive ions coming from the hot wire detector. From observations of the 1, ±1→1, 0 and 2, ±2→2, ±1 transitions for a variety of electric field strengths it was concluded that the principal nuclear molecular interaction was of the type specified by the operator $c\mathbf{I}\mathbf{·}\mathbf{J}$, where $c$ is a constant, $I$ is the spin of the F nucleus, and $J$ is the rotational quantum number. The effects of the ${\mathrm{Li}}^6$ quadrupole and I·J interactions were below the limits of observation. The constant $\frac{c}{h}$ was found to be +37.3±0.7 kc/sec for both transitions. This value is approximately twice that calculated from molecular beam magnetic resonance experiments at strong fields. Using the electric resonance strong field data, calculations determined the constant ${\mu }^{2}A$ to be (747.2±0.9)×${10}^{-76\mathrm{}}$ cgs units for the lowest vibrational state. This quantity for the next vibrational state was greater by (4.3±0.1) percent. $\mu$ is the electric dipole moment, and $A$ is the moment of inertia of the molecule.