1. Univ. Artois, CNRS, Centrale Lille, Univ. Lille, UMR 8181, Unité de Catalyse et Chimie du Solide (UCCS), F-62300 Lens, France
2. Univ. Lille, CNRS, Centrale Lille, Univ. Artois, UMR 8181, Unité de Catalyse et Chimie du Solide (UCCS), F-59000 Lille, France
3. Physics Program, Department of Math. Stat. and Physics, College of Arts and Sciences, Qatar University, P. O. Box: 2713, Doha, Qatar