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.

λ 10-6m J+1 -> J R(nm) 179.62 2-1 .1146 119.90 3-2 .1147 90.03 4-3 .1148 72.140 5-4 .1149 60.247 6-5 .1150

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.