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 {sup 32}S{sup 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{plus minus}0.08 ns for the Ar{sub 2}{sup 2+} molecule and a rate coefficient {ital k}{sub 3}=(1.46{plus minus}0.12){times}10{sup {minus}30} cm{sup {minus}6}/s for the reaction Ar{sup 2+}+2Ar{r arrow}Ar{sub 2}{sup 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.