Rare gas alkali ionic excimers

[摘要] The rare gas alkali ionic molecules are established as a new class of ionic excimers which emit in the vacuum ultraviolet (VUV) regime of the electromagnetic spectrum. Temporal and spectral characteristics of these species with (XeRb)$sp{+}$ at 164 nm and (XeCs)$sp{+}$ at 160 nm have been investigated by soft x-ray excitation in a laser-produced plasma and by high energy pulsed electron beam pumping in this work. Soft x-ray pumping of XeF(B $o$ X) and (XeRb)$sp{+}$ yielded the first observation of excimer molecules formed by reactive kinetics in a laser-produced plasma.The spectrum of (XeRb)$sp{+}$ was observed. The spectral structure could be assigned to 3 dipole allowed transitions originating from the 0$sp{+}$(II), 1(II), 1(I) upper states ending in the 0$sp{+}$(I) ground state. A kinetic study of electron beam pumped mixtures of Ar/Xe/Rb and Ar/Xe/Cs was performed. The observed temporal decays of (XeRb)$sp{+}$ and (XeCs)$sp{+}$ were analyzed. The results suggest that electron deactivation is surprisingly not a dominant quenching process for rare gas alkali ions.The radiative lifetimes are 150 $pm$ 50 ns for (XeCs)$sp+$ and 250 $pm$ 50 ns for (XeRb)$sp+$. In addition several quenching rate constants were extracted from the experimental results. These rate constants and lifetimes were incorporated into a kinetic model for these species. This kinetic model reproduced the experimental observations well providing the electron quenching rate coefficient is kept to a maximum of 5 $imes$ 10$sp{-9}$ cm$sp3$s$sp{-1}$. Estimates for the upper state densities were computed using this model to be $sim$4 $imes$ 10$sp{15}$ cm$sp{-3}$ for (XeCs)$sp+$ and 2 $imes$ 10$sp{15}$ cm$sp{-3}$ for (XeRb)$sp+$. Including absorption due to the photoionization of the alkali atoms, the net gain coefficients are computed to be on the order of 10$sp{-2}$ cm$sp{-1}$. Therefore the rare gas alkali ionic excimers appear to be a promising class of candidates as storage media for VUV lasers.

[发布机构] Rice University

[效力级别] physics