1. Institute for Physical and Theoretical Chemistry, Universität Erlangen, 91058 Erlangen, Germany, Dipartimento di Chimica “G. Ciamician”, Università di Bologna and INSTM, Via Selmi 2, 40126 Bologna, Italy, Radiation Laboratory, University of Notre Dame, Notre Dame, Indiana 46556, and Chemistry Department, University of Sussex, Brighton BN1 9QJ, U.K.