Electron-impact excitation rates in a capacitively coupled 13.6-MHz rf argon discharge were derived from optical emission measurements with high time and space resolution. A propagating excitation wave form is shown to exist at gas pressures as high as 1.0 Torr. The observed features—including temporal broadening of the wave form—are in agreement with recent simulation results, and can explain apparent transitions in electron energy distributions previously reported.

• Received 12 December 1990

DOI:https://doi.org/10.1103/PhysRevLett.66.1858