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

Abstract

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.

Excimer formation mechanism in gaseous krypton and Kr/N2 mixtures

“…Because of its high rate R~--k~-[Kr] > 5 ns-1 in the pressure range considered here (k~=7.8-10 -H cm 3 s -1 [3]), the vibrational relaxation is not included in the scheme. For the same reason collisional-induced predissociation of the 0 + (v' >>0) state was also rejected [8].…”

“…We believe that both the upward dissociation of Kr* (1,)v,>>0 and collisional-induced predissociation of Kr* (0u) v,>>0 populate the precursor states. Though a threshold value for the predissociation was estimated in [8] to be 2 c~ 124.7 nm, because of the large bandpass of the monochromator used (A)~ ~0.7 nm) the true position of )~c may be shifted to longer wavelengths.…”

“…The high pressure limit (p=>l atm) is considered in [3,8]. In [8,9] excitation of the resonant 3P 1 atomic level is used for the observation of the II. continuum (145 nm).…”

“…More reliable information about excited state kinetics has been obtained with optical selective excitation [3,[8][9][10][11][12]. The high pressure limit (p=>l atm) is considered in [3,8].…”

Environmental influence on the IR fluorescence of Xe2* molecules in electron beam excited Ar–Xe mixture at high density

“…The physical processes leading to excimer fluorescence in rare gases in low density limit are very well known [3,4,12,13,14,15,16,17,18,19,20]. The potential curve of diatomic rare gas molecules in the ground state is repulsive except for a weak van der Waals attraction.…”