1. Department of Physics, Umeå University, 901 87 Umeå, Sweden, Ion Cyclotron Resonance Program, National High Magnetic Field Laboratory, Tallahassee, Florida 32310-4005, Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, Institute of Problems of Chemical Physics, RAN, 142432 Chernogolovka, Moscow Region, Russia, and Department of Structural Chemistry, Stockholm University, Stockholm, Sweden