1. Department of Physics, University of Pavia, Via Bassi 6, Pavia (PV) 27100, Italy
2. INFN, Istituto Nazionale di Fisica Nucleare–Pavia Unit, Via Bassi 6, Pavia (PV) 27100, Italy
3. Department of Chemistry, University of Florence, Sesto Fiorentino (FI) 50019, Italy
4. Centro Grandi Strumenti, University of Pavia, Via Bassi 21, Pavia (PV) 27100, Italy
5. Department of Physics, University of Milan, Via Celoria 16, Milan (MI) 20133, Italy
6. INFN, Istituto Nazionale di Fisica Nucleare–Milan Unit, Via Celoria 16, Milan (MI) 20133, Italy