FAR INFRARED LASER MAGNETIC RESONANCE SPECTRUM OF CH

Author Institution: National Bureau of StandardsLaser magnetic resonance spectra between 0 and 17 kG have been recorded and analyzed for $(J^{\prime} - J^{\prime\prime}) = (7/2 - 5/2), (5/2 - 3/2)$, and (3/2 - 1/2) transitions in the CH molecule, using the optically pumped far infrared lasers: $118.8\,\mu m (CH_{3}OH), 180.7\,\mu m (CD_{3}OH), 554.4\,\mu m (CH_{2}CF_{2}) 561.3\,\mu m (DCOOD)$, and $567.9\,\mu m (CH_{2}CHCl)$. Other transitions in CH were detected with the $^{13}CH_{3}OH$ laser at 115.8, 149.3 and $203.6\,\mu $m. The CH radical was generated in a low-pressure methane and atomic fluorine flame within the laser cavity. Analysis of the $M_{J} {^{\prime}} - M_{J}{^{\prime\prime}}$ structure yields wave-numbers for the rotational transitions mentioned above of 84.3494, 55.3397, and $17.8376\, cm^{-1}$, respectively. Combining results from the $M_{J}$ analysis with the $J = 1/2$ A-doubling interval derived from radioastronomy measurements yields A-doubling values for the $J = 3/2, 5/2$, and 7/2 states of 0.0237, 0.1620, and $0.3759\, cm^{-1}$, respectively. Both the rotational intervals and the A-doublings are in good agreement with earlier less precise optical results. Analysis of the hyperfine structure yields values for the Frosch and Foley hyperfine parameters of $a = +52, b = -74, c = +52$ and $d = +43.6$ MHz, in good agreement with recent ab initio estimates and radio-astronomy measurements