1. Department of Chemistry and
Biochemistry, University of Berne, Freiestrasse
3, CH-3012 Berne, Switzerland
2. Instituto de Física, Benemérita Universidad Autónoma de Puebla, Apartado Postal J-48, Puebla
72570, Mexico
3. Department of Physics, Lancaster University, Lancaster LA1 4YB, United Kingdom
4. Departamento de Física, Universidad de Oviedo and CINN (CSIC), ES-33007 Oviedo,
Spain