1. Department of Chemistry, University of Sheffield, Sheffield, S3 7HF, United Kingdom, Department of Chemistry, University of Warsaw, Al. Zwirki i Wigury 101, PL 02-089 Warsaw, Poland, Afdeling Kwantumchemie, Departement Chemie, Katholieke Universiteit Leuven, Celestijnenlaan 200F, B-3001 Heverlee, Belgium, and Eastman Kodak Research Laboratories, 1999 Lake Avenue, Rochester, New York 14650