1. Contribution from the Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan, Research Centre for Spectrochemistry, Graduate School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan, Electrotechnical Laboratory, Umezono, Tsukuba 305-0045, Japan, and Equipe Précurseurs Moléculaires et Matériaux, LCC-CNRS, 205 Route de Narbonne, 31077 Toulouse Cedex 04, France