1. J.W. Emsley and G.R. Luckhurst, Mol. Phys., 40, 19 (1980).
2. E.E. Burnell and C.A. de Lange, J. Chem. Phys., 76, 3474 (1982).
3. J.G. Snijders and C.A. de Lange, J. Chem. Phys., 77, 5386 (1982).
4. D. Catalano, C. Forte and C.A. Veracini, to be published.
5. J.W. Emsley, G.R. Luckhurst and G.N. Shilstone, unpublished results.