1. Adamson, A. J., Whittet, D. C. B., and Duley, W. W.: 1990,M.N.R.A.S. 243, 400–404.
2. Agarwal, V. K., Schutte, W., Greenberg, J. M., Ferris, J. P., Briggs, R., Connor, S., Van de Bult, C. P. E. M., and Bass, F.: 1985,Origins of Life 16, 21.
3. A'hearn, M. F., Hoban, S., Birch, P. V., Bowers, C., Martin, R., and Klinglesmith, D. A., III: 1986,Nature 324, 649.
4. Allamandola, L. J., Greenberg, J. M., Norman, C. A., and Hagen, W.: 1980, ‘Proc. IAU Symposium no. 87 on Interstellar Molecules’, Andrew, B. H. (ed.), Kluwer Acad. Publ., Dordrecht, pp. 373–380.
5. Anders, E. and Owen, T.: 1977,Science 198, 453–65.