The decay dynamics of photoexcited rare gas cluster ions J. Chem. Phys. 111, 959 (1999); 10.1063/1.479378 A selected-ion-flow-drift-tube study of charge transfer processes between atomic, molecular, and dimer ion projectiles and polyatomic molecules ethane, propane, and n-butane Kinetics associated with the decay of the low-lying excited states of xenon is investigated in a density range 2.S X 10 18 to 2.S X 10 20 atoms cm -3 (pressure range between 10 4 and 10 6 Pa). Three different experiments are performed, i.e., two-photon excitation of 6p atomic states or ot molecular states, VUV one-photon excitation of the 6s[ 3/2] I and 6s' [ 112] I atomic states, and laser probing of intermediate transient species. The basic experimental data are the timeresolved second continuum excimer fluorescence at -173 nm and the photoionization current. It is found that all excitation decays through 6s[3/2] lor 6s[3/2Jz with a branching ratio 9/1. Part ofthe 6s[3/2] I species (70%) decay subsequently via the 6s[3/2Jz 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: /6s[3/2] I and luOu-/6s[3/2]z is rejected. The data treatment, with the help of 2 or 2 X 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:, v::::::0/6s[3/2] I relaxed excimer lifetime is found to be 4.S(5) ns, and that ofthe lu,O; /6s[3/2Jz state 103(2)ns.

Kinetics associated with the decay of low lying excited states of argon is investigated in a pressure range up to 4 X 10 6 Pa. Selective pulsed vacuum-ultraviolet excitation is used for the first time for a kinetic study of argon allowing a rather detailed analysis. The results are deduced from time resolved total luminescence of the well-known second continuum which is associated with the lowest excimer states 0,,+ eP I ) and 1",0; ep 2 ) , having fast and slow radiative decays, respectively. A different ratio of the fast to the slow component is observed when exciting in the high or in the low energy side of the first self-broadened line, the IS O --+3P I transition centered at 106.6 nm, quite similar to what has been reported for xenon. The kinetic model introduced by Wenck et al. for xenon [Chem. Phys. Lett. 66, 138 (1979)] is the only one that agrees with the observed time and pressure dependences. In this model, the decay of the atomic state 3P I leads to efficient population of 1", 0; ep 2 ) , via 0: eP I ), and 1 9 , Og-ep 2 ), molecular states and the atomic state 3P 2 • The radiative lifetime of the (1",0;) excimer state is presently determined to be 3.15(5) fts. The decay associated with IP I excitation is more complicated since it involves more intermediate steps. No difference is detected when exciting in the low or in the high energy side of the corresponding selfbroadened line. That result, together with the time behavior, allows one to conclude that the atomic state 3 Po is efficiently populated in the decay sequence, thus introducing a rather long lived reservoir effect. Such an effect is totally different from what was reported for xenon in which collision coupling with the nearby 6p levels plays a major role. 4576

Kinetics associated with the decay of the 5s[3/2]01 (3P1) excited state of krypton is investigated using selective excitation, in the density range 2.5×1018 to 375×1018 atoms cm−3 (pressure from 104 to 1.5×106 Pa). The vacuum ultraviolet (VUV) one-photon excitation around 123.6 nm is provided by monochromatized light from a laser-generated rare gas plasma. The basic experimental data are obtained through the time-resolved second continuum excimer fluorescence at 145 nm. When initial conditions give purely 3P1 atomic excitation a single slow component is observed at densities up to 15×1018 cm−3, corresponding to the 1u,0−u, v=0 excimer radiative decay (265 ns). From 15 to 60×1018 cm−3, a second fast component shows up, corresponding to the 0+u(3P1), v=0 excimer radiative decay. Above 60×1018 cm−3 the intensity ratio between the two components remains constant (F/S≊0.21). Behavior rather similar to that previously reported for argon and xenon is found. In particular one concludes that the 3P2 atomic state plays a major role as an intermediate state in the 1u,0−u dimer formation whereas possible short-distance attractive g states do not seem to play any significant role. A self-consistent analysis leads to a detailed quantitative description of the kinetics. In particular, it is found that dimer formation times from 3P1 and 3P2 atomic states are in the ratio 3/1. In the considered density range collisional rates are found to vary quadratically.

Four even-parity atomic series corresponding to transitions from the Ss'[1/2]~level to the ('P3/p)np, nf levels of krypton have been observed, using a resonant multistep two-color photoionization method. The energies of 7p'[3/2]"7p'[1/2]~, 7p'[3/2]"7p'[1/2]0, np [1/2)"np [3/2]" np [1/2]0, and nf [3/2], 2 levels are determined and the principal quantum numbers are calculated for n up to 45, 32, 49, and 44, respectively. Strong spectral irregularities in intensity and position are analyzed with the help of Lu-Fano diagrams and multichannel quantum defect theory in the case of the most intense Ss'[1/2]o~np [1/2]o series. Density shift rates have the constant value of -7.4(2)X10 ' cm '/cm ' for the s~p high-n series members, outside regions where irregularities are observed, in agreement with existing doped krypton data. A close agreement with the Fermi model is obtained for these high-n members of regular series. Departure from this agreement is found for members whose excited levels are mixed with 7p' states. A clear relationship between the p -p admixture and shift rate decrease, in regions of irregularities, is demonstrated.

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