Observational study of reactive ions and radicals in PDRs A. Fuente, A. Rodrıguez-Franco, S. Garcıa-Burillo, J. Martın-Pintado and J. H. Black A&A, 406 3 (2003) 899-913 Published online: 17 November 2003 DOI: 10.1051/0004-6361:20030712