In the experiment on electron-stimulated positive-ion desorption, H+(NH3) ions are ejected intensively from NH3 physisorbed on an Ar spacer layer, whereas fragmentation occurs preferentially for C2H6, C2H4, and C2F6 molecules. The ions are emitted efficiently via Coulombic fission of physisorbed ultrathin films of NH3, C2H6, and C2H4, but dissociative ionization is responsible for the ion emission from the C(2)F(6)layer. Moreover, molecular reactions are induced explosively by the electronic excitation of physisorbed ultrathin films: solvated protons or deuterons of formamide, ethyl amine, and ethyl alcohol, respectively, are ejected from CO/NH3, C2H6/NH3, and C2H6/D2O layers. (C) 2003 Elsevier B.V. All rights reserved.