Fourier transform emission spectroscopy with supersonic jets

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Abstract
The 4f → 3d and 4f → 4s Rydberg → Rydberg transitions of NO in emission from a supersonic jet discharge have been recorded by Fourier transform spectrometry. Both the 4f → 3dσ,π and 4f → 3dδ subbands at 5100 and 5800 cm-1, respectively, of the 4f → 3d 0-0 and 1-1 transitions have been analysed with the help of calculated spectra and by making use of the known spin splittings of the lower levels. The considerably weaker 4f → 4s 0-0 and 1-1 bands at 6930 cm-1 appear on account of the strong interaction of 4sσ with 3dσ. The effects of an avoided crossing between the 3dπ+, F 1 and 3dπ-, F 2 levels on the 4f → 3d emission intensities are examined and compared with similar effects on the 3d ← X 2Π absorption spectra. The lack of emission from a number of 4f levels is attributed to predissociation mediated by the 4sσ and 4dσ states. The various band types are discussed that occur in Rydberg → Rydberg transitions of NO.