Excitation of H2 in photodissociation regions as seen by Spitzer E. Habart, A. Abergel, F. Boulanger, C. Joblin, L. Verstraete, M. Compiègne, G. Pineau des Forêts and J. Le Bourlot A&A, 527 (2011) A122 Published online: 08 February 2011 DOI: 10.1051/0004-6361/20077327