Example CH, ²Π_r

CH has a ²Π_r ground state; the ²Π_1/2 state is lower in energy. CH is well described by Hund's case (b), because A is only about twice as big as B. However, the magnitude of A causes N not to be a "good" quantum number, in particular for low values of N. This results in significant intensities for transitions with ΔJ = 1 and ΔN = 0 (spin-rotation transitions) or ΔN = 2.

The fit is based on the λ-doubling transitions reported in (1) M. Bogey, C. Demuynck, and J. L. Destombes, Chem. Phys. Lett. 100 (1983) 105–109; (2) C. R. Brazier and J. M. Brown, Can. J. Phys. 62 (1984) 1563–1578 and references therein; the N = 1 spin-rotation transition near 535 GHz, reported by (3) T. Amano, Astrophys. J. 531 (2000) L161–L164; as well as the pure rotational transitions by (4) S. A. Davidson, K. M. Evenson, and J. M. Brown, Astrophys. J. 546 (2001) 330–337.

The new dataset takes into consideration (5) M. C. McCarthy, S. Mohamed, J. M. Brown, and P. Thaddeus, Proc. Nat. Acad. Sci. 103 (2006) 12263–12268.

The λ-doubling transitions not only determine the respective parameters, but also the hyperfine structure constants and, to some extent, A. The transitions from (3) and (4) result in A, B, γ as well as the centrifugal distortion corrections for the latter two parameters.

• CH.lin contains the experimental lines, etc.
• CH.par is the parameter file.
• ch.int limits the calculation of lines according to intensities, quantum numbers etc. It also contains the dipole moment components.

The following files are also available:

• CH.fit, the fit file (a documentation of the fitting procedure; also given are the parametersmeter with uncertainties along with correlation coefficients);
• development of the parameter values and its uncertainties because of changes in the parameter file or in the line file;
• CH.cat, new predictions;
• CH.out, documentation of the prediction;
• CH.egy, the enrgy file;
• CH.mrg: file with predictions (in MHz), in which the observed frequencies are given with experimental uncertainties;
• and finally CH.wvn, basically the same file, but frequencies and uncertainties in cm^–1.