Rotational Spectrum of CH+
The instrument called the Long Wavelength Spectrometer (LWS) in the Infrared Space Observatory detected emission lines associated with the pure rotational spectrum of CH+. The measurements show the rotational transitions characteristic of diatomic molecules. The rotational spectrum shows some centrifugal stretching as indicated by the calculated bond length in the table.
For high rotational transitions, the molecule must be treated as a non-rigid rotor.
The spectral lines of CH+ reported above were observed in the planetary nebula NGC 7027. From relative intensities of the transitions a rotational temperature of 150 +/- 20 K was reported. A relative abundance CH+/CO of 2 to 6x10-4 was implied from the data.
Reference: "Discovery of Far-IR Pure Rotational Transitions of CH+ in NGC7027", Cernicharo, J., Liu, X.-W., Gonzalez-Alfonso, E., Cox, P., Barlow, M.J., Lim, T., Swinyard, B.M., Astrophysical Journal Letters v.483, p. L65, 1997.