1997A&A...317L..55D

We report the detection of CN, HCN, HNC, CS, HCO⁺, C₂H and H₂CO (ortho and para) in the protoplanetary disks of DM Tau and GG Tau. For the first time organic molecules are observed in objects representative of the presolar nebula. These molecules are underabundant with respect to the standard dense clouds. The depletions in the "outer" disk of DM Tau (100<r<900AU), derived from the line intensities and state of excitation, range from f∼5 (for CO) to 100 (for H₂CO). The relatively large abundances of CN and C₂H are typical of a photon-dominated chemistry.