Electron-stimulated reactions in solid films of cyclopropane, condensed on Ar spacers deposited on a Pt substrate, were induced and monitored simultaneously using a high-resolution electron-energy-loss spectrometer. Absolute cross sections for the formation of propene, including similar unsaturated species, were independently determined as sigma(p) = (7.2 +/- 3.9) x 10(-17) cm(2) and sigma(p) = (9.6 +/- 4.8) x 10(-17) cm(2) at an incident electron energy of 15 eV using both characteristic electronic and vibrational energy losses, respectively. The cross section obtained as a function of the film thickness of cyclopropane deposited on a fixed 5-layer spacer of Ar was found to increase above 3-layer coverage. This suggests that intermolecular reactions are not only involved, but also increase the production rate of unsaturated compounds in multilayer films.