Recent analyses of the spectrum of the planetary nebula NGC 7027 by Péquignot & Baluteau (1994), Baluteau et al. (1995) and Péquignot (1996) have stimulated the present calculation of term energies, wavelengths and oscillator strengths for transitions involving Rydberg states of C II, C III and C IV for values of the principal quantum number up to n = 30. Our results have been compared with the NGC 7027 spectrum observed in the 654-1046 nm region by Baluteau et al. (1995) and wavelength predictions to an accuracy of at least a few 0.01 nm have been obtained for lines which might be detectable in smaller wavelength regions. Several of our predicted lines coincide with many lines observed in the unpublished NGC 7027 spectrum between 400 and 654 nm (Péquignot 1997).
Acknowledgements
Financial support from the Belgian Fund for Scientific Research (F.N.R.S.) is acknowledged. It is also a pleasure to thank Dr. Péquignot (Meudon) for providing us with unpublished spectra of NGC 7027.