1. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge,
Massachusetts 02138, United States
2. Department of Chemistry, Wesleyan University, Middletown, Connecticut 06459,
United States
3. I. Physikalisches
Institut, Universität zu Köln, Zülpicher
Strasse 77, 50937 Köln, Germany