Pressure-dependent decay of the 3p54p configuration in argon excited by alpha-particles and protons

The pressure dependence of the decay of the Ar(3p(5)4p) states excited by an energetic pulsed ion beam was studied in the pressure range 5-1600 kPa. All of the ten 3p(5)4p states have a fast build-up component and, with the exception of the 2p(1) state, two decay components: one fast (3-18 ns at 100 kPa) and one slow (20-300 ns at 100 kPa). Extrapolation of the fast decay rates to zero pressure yields the natural lifetimes of the states to values within the accuracy of the measurements. Most of the slow decays show nonlinear pressure dependencies. This nonlinearity is probably due to several competing processes. The slow decay of the 2p(3)-2p(5) states can be associated with the fast decay of the 2p(2) state. The pressure dependency of the 2p(2) state is considerably different from the other states within the 3p54p configuration. It is concluded that the build-up of the 2p(2) state is associated with dissociative recombination of Ar-2(+) and Ar-3(2+) molecules.