1. Department of Chemistry, Stanford University, Stanford, California 94305-5080, Institute of Mathematical Statistics, Casa Academiei Romane, Calea Septembrie 13, 76100 Bucharest, Romania, Institute of Physical Chemistry, Romanian Academy, Splaiul Independentei 202, Bucharest 79611, Romania, and Department of Physical Chemistry, University of Bucharest, Bd. Republicii 13, Bucharest 70346, Romania