Molecular Beam Measurement of the Hyperfine Structure of 133Cs19F

The magnitudes and signs of the hyperfine interaction constants for 133Cs19F in the J = 1, v = 0, 1, 2 states have been measured with a molecular beam electric resonance spectrometer. The results for v = 0 are: eQ1q1 = 1.2370(13) MHz, c1 = 0.70(7)kHz, c2 = 15.1(6)kHz, c3 = 0.92(12)kHz, c4 = 0.61(10)kHz. The numbers in parentheses are uncertainties in units of the last digit given. eQ1q1 is the quadrupole coupling constant for the cesium nucleus, c1 and c2 are the spin-rotation coupling constants for the cesium and fluorine nuclei, respectively, and c3 and c4 are the coupling constants for the tensor and scalar parts of the nuclear spin—spin interaction. These constants are obtained from the radio-frequency spectrum of CsF taken under veryweak-field conditions (Edc = 1.5 V/cm; H<0.05 Oe); some previously ignored contributions of the fluorine spin—rotation interaction and the spin—spin interaction are clearly evident. The observed variation in eQ1q1 with vibrational state shows only qualitative agreement with theory. An appendix gives compact expressions for the very-weak-field hfs energy levels of a 1Σ molecule in which only one nucleus has a quadrupole moment.