1. Physical Institute, University of Tübingen, D-7400 Tübingen, FRG
2. Peinke Physical Institute, University of Tübingen, D-7400 Tübingen, FRG
3. Institute for Physical and Theoretical Chemistry, University of Tübingen, D-7400 Tübingen, FRG
4. Institute for Chemical Plant Physiology, University of Tübingen, D-7400 Tübingen,
5. Physical Institute, University of Bayreuth, D-8580 Bayreuth, FRG