1. Department of Chemistry and Biochemistry; Northern Illinois University; DeKalb IL 60115 USA
2. Department of Chemistry and Centre for Research in Mass Spectrometry; York University; Toronto ON M3J 1P3 Canada
3. Department of Chemistry and Biochemistry; University of Windsor; Windsor ON N9B 3P4 Canada
4. Laboratoire de Chimie Physique; Université Paris-Sud; UMR8000 CNRS; 91405 Orsay France