With electron beam, the third continuum of argon, which centers at 240 nm, has been obtained. Then photomultiplier has been used to measure the temporal evolution of 240 nm. The results show that the width of the temporal evolution at 240 nm is larger than the width of the current waveform. In theory, the kinetics model of the argon ionic excimer pumped by electron beam is built. And the relation between density of argon ionic excimer and time is obtained. The effect of the reactions on production of ionic excimer is discussed. The results of theory and experiment show that the time behavior of 240 nm is same as the density of Ar+2 ionic excimer. Therefore, the spectrum around 240 nm should be emitted by Ar+2 ionic excimer.