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Physical Review A

Rb*Hen exciplexes in solid He4

A. Hofer, Peter Moroshkin, Daniel Nettels, Simone Ulzega, Antoine Weis

Published Sep 29, 2006• 20 citations
Publisher

Abstract

We report the observation of emission spectra from ${\mathrm{Rb}}^{*}{\mathrm{He}}_{n}$ exciplexes in solid $^{4}\mathrm{He}$. Two different excitation channels were experimentally identified, viz., exciplex formation via laser excitation to the atomic $5{P}_{3∕2}$ and to the $5{P}_{1∕2}$ levels. While the former channel was observed before in liquid helium, on helium nanodroplets, and in helium gas by different groups, the latter creation mechanism occurs only in solid helium or in gaseous helium above $10\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The experimental results are compared to theoretical predictions based on the extension of a model, used earlier by us for the description of ${\mathrm{Cs}}^{*}{\mathrm{He}}_{n}$ exciplexes. We also report the observation of fluorescence from atomic rubidium in solid helium, and discuss striking differences between the spectroscopic features of $\mathrm{Rb}\text{\ensuremath{-}}\mathrm{He}$ and $\mathrm{Cs}\text{\ensuremath{-}}\mathrm{He}$ systems.

DOI
10.1103/physreva.74.032509

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We report the observation of emission spectra from Rb∗Hen{\mathrm{Rb}}^{*}{\mathrm{He}}_{n}Rb∗Hen​ exciplexes in solid 4He^{4}\mathrm{He}4He. Two different excitation channels were experimentally identified, viz., exciplex formation via laser excitation to the atomic 5P3∕25{P}_{3∕2}5P3∕2​ and to the 5P1∕25{P}_{1∕2}5P1∕2​ levels. While the former channel was observed before in liquid helium, on helium nanodroplets, and in helium gas by different groups, the latter creation mechanism occurs only in solid helium or in gaseous helium above 10K10\phantom{\rule{0.3em}{0ex}}\mathrm{K}10K. The experimental results are compared to theoretical predictions based on the extension of a model, used earlier by us for the description of Cs∗Hen{\mathrm{Cs}}^{*}{\mathrm{He}}_{n}Cs∗Hen​ exciplexes. We also report the observation of fluorescence from atomic rubidium in solid helium, and discuss striking differences between the spectroscopic features of Rb\ensuremath-He\mathrm{Rb}\text{\ensuremath{-}}\mathrm{He}Rb\ensuremath-He and Cs\ensuremath-He\mathrm{Cs}\text{\ensuremath{-}}\mathrm{He}Cs\ensuremath-He systems.
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We report on the systematic observation of emission spectra of Rb∗Hen{\mathrm{Rb}}^{*}{\mathrm{He}}_{n}Rb∗Hen​ exciplexes (n=1,2,…,6),(n=1,2,\dots{},6),(n=1,2,…,6), realized by exciting Rb atoms to the 52P{5}^{2}P52P states (Rb∗)({\mathrm{Rb}}^{*})(Rb∗) in a cold 4He{}^{4}\mathrm{He}4He gas. The observed broad spectral components are assigned to Rb∗Hen{\mathrm{Rb}}^{*}{\mathrm{He}}_{n}Rb∗Hen​ (n=1−−6)(n=1--6)(n=1−−6) using theoretical spectra obtained from ab initio potential curves. The dynamics of the exciplex formation is discussed, based on the observed temperature dependence of the spectra. The He gas density dependence of the spectra of Rb∗He{\mathrm{Rb}}^{*}\mathrm{He}Rb∗He is understood as a change in the population distribution over the vibrational levels. The present results are compared with our previous work with Cs [K. Enomoto et al., Phys. Rev. A 66, 042505 (2002)], and differences are explained in terms of the difference in the fine-structure splitting. Furthermore, we show the emission spectrum observed after the excitation of Rb in liquid He and conclude that it is the fluorescence from the exciplex Rb∗He6.{\mathrm{Rb}}^{*}{\mathrm{He}}_{6}.Rb∗He6​.
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