1. Interstellar Dust, IAU Symposium 135, ed. L. J. Allamandola and A. G. G. M. Tielens, Kluwer, Dordrecht, 1989.
2. Polycyclic Aromatic Hydrocarbons and Astrophysics, ed. A. Lèger, L. B. d'Hendecourt and N. Boccara, Reidel, Dordrecht, 1987.
3. B. T. Draine , in ref. 1, p. 313.
4. C. F. Bohren and D. R.Huffman, in Absorption and Scattering of Light by Small Particles, Wiley, Chichester, 1983, p. 460.
5. Curling and closure of graphitic networks under electron-beam irradiation