Pressure effects on kinetics and decay processes in xenon after selective photoexcitation

Kinetics associated with the decay of the low-lying excited states of xenon is investigated in a density range 2.5×1018 to 2.5×1020 atoms cm−3 (pressure range between 104 and 106 Pa). Three different experiments are performed, i.e., two-photon excitation of 6p atomic states or 0+g molecular states, VUV one-photon excitation of the 6s[3/2]1 and 6s′[1/2]1 atomic states, and laser probing of intermediate transient species. The basic experimental data are the time-resolved second continuum excimer fluorescence at ∼173 nm and the photoionization current. It is found that all excitation decays through 6s[3/2]1 or 6s[3/2]2 with a branching ratio 9/1. Part of the 6s[3/2]1 species (70%) decay subsequently via the 6s[3/2]2 level. The effectiveness of these atomic intermediate steps is directly demonstrated by the transient laser probing. This result, the time analysis, and the discussion allow to set a clear basis to the involved processes and to rule out part of the models proposed in the literature. In particular, the hypothesis of infrared decay from attractive high-lying molecular states to the lowest lying excimer states 0+u /6s[3/2]1 and 1u0−u /6s[3/2]2 is rejected. The data treatment, with the help of 2 or 2×2 exponential formula depending on density, is discussed. It takes into account the instrumental response so that kinetics information is reached down to the nanosecond range. In particular, the 0+u, v≊0/6s[3/2]1 relaxed excimer lifetime is found to be 4.5(5) ns, and that of the 1u,0−u /6s[3/2]2 state 103(2)ns.