The dissociative ionization of 10 derivatives of 10-sila-2-azaanthracene, containing cyanoethyl (I-III), aminopropyl (IV), amino (V, VI), and amide (VII-X) groups at the C(9) atom, was investigated. It was shown that for all the compounds the general direction of decomposition is elimination of substituents from the silicon and carbon C(9) atoms. The stability of the compounds to electron impact is determined chiefly by the nature of the substituent at the C(9) atoms and depends weakly on the type of substituent at the silicon atom. In the case of amino-derivatives V-X, fragmentation of the molecular ions is determined by the method of localization of the positive charge in the molecular ion. This determines the occurrence of specific decompositions, which permits reliable identification of the compounds studied according to their mass spectra. © 1985 Plenum Publishing Corporation.