Very high rotational excitation of CO in a cooled electric discharge through carbon monoxide

Infrared emission from 12CO and 13CO, excited in the cathode region of a discharge tube immersed in liquid nitrogen, was recorded by Fourier-transform spectrometry at a resolution of 0.005 cm−1. The Δv=1 sequence bands recorded in the 2500–1800 cm−1 spectral interval, indicate the existence of three different rotational populations; (i) molecules in the zero-ground level with Trot≈100 K (responsible for reabsorption of part of the 1–0 emission band); (ii) molecules with Trot≈275 K (maximum intensity for Jmax′≈6 in each band, Tvib≈3000 K for v′=2–4, Tvib≈8600 K for v′=5–13); (iii) molecules with v′ limited to 6, for which R-rotational lines are observed for J′ values between 50 and 120 (Jmax′≈90, non-Boltzmannian population distribution). The full-width at half-maximum (FWHM) of all the observed lines is less than 0.007 cm−1. A Doppler width of 0.005 cm−1 and translational temperature Ttr≈280 K can be deduced. Such high-J levels of the CO molecule had never been observed in the laboratory. In the absorptio...