1. a Los Alamos National Laboratory, Chemistry Division , University of California , Los Alamos , New Mexico , 87545 , U.S.A.
2. b Max-Planck-Institut für Strömungsforschung , D-3400 , Göttingen , Böttingerstrasse 4-8, F.R. Germany
3. c Department of Chemistry , University of California, Irvine , California , 92715 , U.S.A.