1. Departments of Physics and Chemistry, Umeå University, 901 87 Umeå, Sweden, Department of Chemistry, Rice University, Houston, Texas 77251, Ion Cyclotron Resonance Program, National High Magnetic Field Laboratory, Tallahassee, Florida 32310-4005, Institute of Problems of Chemical Physics, RAN, 142432, Chernogolovka, Moscow Region, Russia, and Department of Chemistry, Stockholm University, Stockholm, Sweden