The first decay frequency, 1/r i is attributed to the Xe(3P ) ) state. In this case, 1/k i corresponds to the apparent lifetime of the resonant state (1.„ = 3.98 µs) and k51 is the 3-body rate constant of formation of the Xe[0+„ CPO] excimer. The second one, 1/T2 is attributed to the Xe(3P2) state. Then, 1/1(12 corresponds to the lifetime of the metastable state and k52 is the 3-body rate constant of formation of the Xe 1„ (3P2)] excimer. These results are in good agreement with those obtained with 3-photon selective excitation of Xeelp i ) state [3]. In both cases, no 2-body collision rate constant term is found.
The destruction rates of the xenon $6{s}^{\ensuremath{'}}{[\frac{1}{2}]}_{0}$ metastable and $6{s}^{\ensuremath{'}}{[\frac{1}{2}]}_{1}$ resonance atoms by collisions with ground-state xenon atoms have been measured by studying the temporal dependence of the number densities of the $6{s}^{\ensuremath{'}}$ and
6p atoms. The studies have been made both during the earlier afterglow of a xenon pulsed discharge and after the selective production of the $6{s}^{\ensuremath{'}}{[\frac{1}{2}]}_{0,1}$ atoms by a laser excitation in the late afterglow. An original optical pumping technique, using a tunable pulsed dye laser, was employed to populate the $6{s}^{\ensuremath{'}}{[\frac{1}{2}]}_{0,1}$ levels by excitation of the
6s[23]2 long-lived metastable atoms to $6{p}^{\ensuremath{'}}$ levels. The pressure dependence of the decay frequencies of these $6{s}^{\ensuremath{'}}{[\frac{1}{2}]}_{0,1}$ atoms was analyzed in the xenon pressure range of 0.04 to 1 torr and a kinetic model describing the evolution of the densities of these atoms after their production was established. The rate coefficients for the relaxation of the $6{s}^{\ensuremath{'}}{[\frac{1}{2}]}_{0}$ metastable and $6{s}^{\ensuremath{'}}{[\frac{1}{2}]}_{1}$ resonance atoms by two-body collisions involving a ground-state xenon atom are (8.45\ifmmode\pm\else\textpm\fi{}0.85) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}12}$
cm3 ${\mathrm{sec}}^{\ensuremath{-}1}$ and (6.65 \ifmmode\pm\else\textpm\fi{} 1.00) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}11}$
cm3 ${\mathrm{sec}}^{\ensuremath{-}1}$, respectively. Results show that, in fact, at least 75% of this relaxation is a transfer of population to the
6p[21]1 level following ${\mathrm{Xe}}^{*}(6{s}^{\ensuremath{'}}{[\frac{1}{2}]}_{0,1})+\mathrm{Xe}\ensuremath{\rightleftarrows}{\mathrm{Xe}}^{*}(6p{[\frac{1}{2}]}_{1})+\mathrm{Xe}\ensuremath{-}\ensuremath{\Delta}E$. These collisional transfer processes have been explained by means of Mulliken's xenon molecular potential curves.
At low pressures, excitation is due to the absorption of three photons and causes emission of the resonance line and the related first continuum ( lambda approximately 125 nm). At higher pressures, excitation mainly arises from a photon of the third harmonic of the laser wave and the second continuum ( lambda approximately 148 nm) is detected. Luminescence attenuations in the excitation spectra can be explained by the absorption of a fourth photon. The natural lifetime of the 3 P 1 is determined using Holstein's theory. The role of two and three-body collisions is demonstrated in the decay of the 3 P 1 state as in the role of three-body collisions for the 3 P 2 state. The corresponding rate constants are determined and the lifetime of the 1 u ( 3 P 2 ) state evaluated.
Experiments using monochromated synchrotron radiation revealed that for densities of the order of
1019 atoms/
cm3 and more, xenon exhibits a continuous photoresponse excitation spectrum below the atomic ionization potential (12.12 eV). The lower limit of the continuum is at about 11.10 eV, the energy difference between the ground state of the molecular ion
Xe2+ and that of the free atom. This is attributed to excimer formation at the wings of the atomic absorption lines followed by ionization and creation of xenon dimer ions. Dips appearing in the continuum very near to positions of atomic lines are discussed invoking the quasistatic theory.
The kinetics of formation and decay of Cs-Xe molecules in their $\ensuremath{\Sigma}$ and $\ensuremath{\Pi}$ bound states produced in Cs-Xe mixtures irradiated with a short-pulse dye laser tuned around the $7P\ensuremath{-}6S \mathrm{Cs}$ resonance transition has been investigated by fluorescence decay measurements. The time-resolved spectra of the 4600- and 5720-\AA{} molecular fluorescent bands were studied in relation to xenon density, which ranged from 0.9 to 6.9 amagats. Quantitative collisional cross sections are derived from the measured transition rates with peak values around ${10}^{\ensuremath{-}17}$
cm2.