Chemistry in disks - IV. Benchmarking gas-grain chemical models with surface reactions D. Semenov, F. Hersant, V. Wakelam, A. Dutrey, E. Chapillon, St. Guilloteau, Th. Henning, R. Launhardt, V. Piétu and K. Schreyer A&A, 522 (2010) A42 Published online: 29 October 2010 DOI: 10.1051/0004-6361/201015149