Detection of low-frequency lambda-doublet transitions of the free 12CH and 13CH radicals.

By Fourier transform microwave spectroscopy, lambda-doubling transitions of (12)CH and (13)CH in the lowest rotational levels of the X(2) product operator(1/2) ground state have been directly detected, which has not been done previously. For both radicals, hyperfine-split lines have been measured to an accuracy of better than 1 ppm between 3 and 15 GHz, an improvement of at least 2 orders of magnitude over previous laboratory data. The measured frequencies have been combined with all previous data for CH and (13)CH in the v = 0 level of the X(2) product operator electronic state to determine improved hyperfine parameters. The production of CH from various gases also has been studied and, with methanol, the yield of CH relative to OH. Astronomical studies of CH in higher rotational levels and (13)CH can now be undertaken on the basis of the present work.