1. Institute of Chemistry, GKSS Research Center, Kantstrasse 55, D-14513 Teltow, Germany; A. V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, 29 Leninsky Pr., 117912 Moscow, Russia; and N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 4 Kosygina Str., 117334 Moscow, Russia