Chemistry as a probe of the structures and evolution of massive star-forming regions S. D. Doty, E. F. van Dishoeck, F. F. S. van der Tak and A. M. S. Boonman A&A, 389 2 (2002) 446-463 Published online: 27 June 2002 DOI: 10.1051/0004-6361:20020597