The use of Fourier transform mass spectroscopy is described for the study of volatile products arising from thin organic films upon impact of electrons in the 3-1500-V energy range. Gas pulses emitted from the exposed spot are ionized by electron impact or chemical ionization techniques; the ions are trapped and compositionally analyzed. With poly(butene-1 sulfone) films the energy deposition per pulse required for the observation of the monomer products is <0.1 μJ. Electrons with energy lower than the first allowed optical transition can initiate the depolymerization reaction; in the 20-200-eV range the G value for the depolymerization reaction is 700 ± 300. © 1991 American Chemical Society.