1. Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge,
CB3 0HE, U.K.
2. Department
of Physics, University of New Brunswick, P.O. Box 4400, Fredericton,
E3B 5A3, Canada
3. Department
of Chemistry, University of New Brunswick, P.O. Box 4400, Fredericton,
E3B 5A3, Canada
4. Bragg Institute, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia
5. Department of Chemistry, University of Leuven, Celestijnenlaan 200D, 3001 Leuven,
Belgium
6. Department of Molecular
Science and
Technology, Ajou University, Suwon 443-749,
Korea