1. Department of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ, U.K., University of Surrey Ion Beam Centre, Guildford, Surrey, GU2 7XH, U.K., Institute of Nuclear Research of the Hungarian Academy of Sciences (ATOMKI), H4001 P.O. Box 51, Debrecen, Hungary, and Department of Chemical Engineering, Imperial College London, South Kensington Campus, London SW7 2AY, U.K.