1. Harvard-Smithsonian Center for Astrophysics and School of Engineering & Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States
2. Department
of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309, United States
3. JILA, National Institute of
Standards and Technology, and Department
of Physics, University of Colorado, Boulder, Colorado 80309, United States
4. Institute
for Theoretical Chemistry, Department of Chemistry, The University of Texas at Austin, Austin, Texas 78712, United States
5. I.
Physikalisches Institut, Universität zu Köln, Zülpicher
Str. 77, 50937 Köln, Germany