1. Institut für Physikalische Chemie, Universität Köln, Luxemburger Str. 116, D-50939 Köln, Germany
2. Finnish Meteorological Institute, Sahaajankatu 22E, SF-00810 Helsinki, Finland
3. Department of Chemistry, Faculty of Science, Kyushu University 33, Fukuoka 812-81, Japan
4. Chemistry Department, P.O. Box 5810, Clarkson University, Potsdam, New York 13699-5810