Emissions from Si, SiH, H, Ar, and ArC are investigated for a free supersonic jet of a mixture of monosilane 5% (or 10%) with argon; the jet is activated by electron-beam plasma, and all the emissions are measured as a function of pressure, temperature in the gas source, the nozzle-to-electron beam distance, and the beam current. It is found that for certain parameters a process initiates which inhibits radiation of the spectral lines of Si, SiH, and H, and stimulates radiation of some spectral lines of argon atoms. It is shown that these anomalies are connected with a condensation process in the jet and, apparently, they are caused by electron-induced fluorescence of monosilane-containing clusters. The mechanisms for abnormal emissions of argon atoms and electron-excited fragments of monosilane molecule are suggested.