Third excimer continuum of argon excited by a heavy-ion beam

Abstract

The emission of the third excimer continuum of argon in the wavelength range between 175 and 250 nm has been studied by time-resolved optical spectroscopy. Argon gas at pressures between 5 and 100 kPa was excited with a pulsed beam of 100-MeV $^{32}\mathrm{S}^{9+}$ ions from the Munich tandem van de Graaff accelerator. Wavelength spectra recorded in different time windows after the 2-ns beam pulses show that two different components contribute to the third continuum of argon. A radiative lifetime of 5.71\ifmmode\pm\else\textpm\fi{}0.08 ns for the ${\mathrm{Ar}}_{2}^{2+}$ molecule and a rate coefficient ${\mathit{k}}_{3}$=(1.46\ifmmode\pm\else\textpm\fi{}0.12)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}30}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}6}$/s for the reaction ${\mathrm{Ar}}^{2+}$+2Ar\ensuremath{\rightarrow}${\mathrm{Ar}}_{2}^{2+}$+Ar were determined from the pressure dependence of time spectra at a wavelength of 190 nm. Additional time spectra were measured at 210 and 230 nm.