Pulse radiolysis and emission spectroscopy techniques have been used to examine the production of the 2p(1) state of Ar and the 4p P-2(1/2) and 4p D-2(5/2) states of Ar+ at gas pressures below 1 Torr. The rate of formation of these states has been compared with the results from calculations using the time-dependent Spencer-Fano theory of high-energy electron degradation. It is found that the theory successfully predicts the time scale of events in pulse-irradiated argon gas.