1. a Department of Chemistry , University of Keele , Keele, Staffordshire ST5 5BG, England
2. b The Atlas Centre, Rutherford Appleton Laboratory Chilton , Didcot, Oxfordshire OX11 0QX, England
3. c Department of Physics , University of Keele , Keele, Staffordshire, ST5 5BG, England
4. d Computer Centre , University of Keele , Keele , Staffordshire , ST5 5BG , England