Electron stimulated desorption (ESD) of fragment anions from condensed multilayer XCN films (X = Br, Cl) deposited on a cryogenically cooled gold crystal shows two pronounced resonant structures located near 4.4 and 8.8 eV indicating that the process is driven by dissociative electron attachment (DEA). These features do not have gas phase analogues and demonstrate the strong effect of the environment on negative ion formation from XCN. This behaviour is interpreted to arise from particular electronically excited resonances, namely shape resonances (barely visible in gas phase DEA due to their short lifetime) which are converted into long-lived Feshbach resonances in the condensed phase. (c) 2005 Elsevier B.V. All rights reserved.