Considerable changes were made in the transition frequency set of CH with respect to the first two entries from Mar. 2000 and Sep. 2006, respectively. As usually, only the most accurate data were retained for transition frequencies reported with microwave accuracy. The parameter set is identical to the previous CDMS entry and was cited and used in
(1) M. A. Martin-Drumel, O. Pirali, D. Balcon, P. Bréchignac, P. Roy, and M. Vervloet, 2011, Rev. Sci. Instrum. 82, Art. No. 113106.
Several far-infrared transitions were reported in that work. The hyperfine parameters were greately improved through the Λ-doubling transition frequencies from
(2) S. Truppe, R. J. Hendricks, S. K. Tokunaga, E. A. Hinds, and M. R. Tarbutt, 2014, J. Mol. Spectrosc. 300, 70.
Further Λ-doubling transition frequencies were reported by
(3) M. C. McCarthy, S. Mohamed, J. M. Brown, and P. Thaddeus, 2006, Proc. Nat. Acad. Sci. 103, 12263;
by
(4) M. Bogey, C. Demuynck, and J.-L. Destombes, 1983, Chem. Phys. Lett. 100, 1055;
and by
(5) C. R. Brazier and J. M. Brown, 1983, J. Chem. Phys. 78, 1608.
Two hyperfine components of the ground state spin-flip transition near 533  were reported by
(6) S. Truppe, R. J. Hendricks, E. A. Hinds, and M. R. Tarbutt, 2014, Astrophys. J. 780, Art. No. 71.
In combination with (2), the hyperfine components near 537 GHz are constrained about 100 kHz lower than initially reported. Mostly rotational transitions were reported by
(7) S. A. Davidson, K. M. Evenson, and J. M. Brown, 2001, Astrophys. J. 546, 330.
Microwave transitions with uncertainties of 100 kHz or more as well as the FIR transitions were not merged.
CH is well described by Hund's case (b), and the constants used in the fit are essentially those of (2). Since CH is not particularly rigid, the predicted uncertainties for transitions involving higher quantum numbers should be viewed somewhat cautiously.
The dipole moment was taken from
(8) D. J. Phelps and F. W. Dalby, 1966, Phys. Rev. Lett. 16, 3.