1. Institute of Physical and Theoretical Chemistry, University of Tübingen, Auf der Morgenstelle 8, 72076 Tübingen, Germany, Scientific Research Institute for Physical and Chemical Problems, Belarus State University, Leningradskaya 14, 220050 Minsk, Belarus, and Istituto per la Microelettronica e i Microsistemi, IMM-CNR, Sezione di Lecce, Via Arnesano, 73100 Lecce, Italy