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Physical Review A

Emission spectra of Cs-He excimers in cold helium gas

Katsunari Enomoto, Keiichi Hirano, M. Kumakura, Yoshiro Takahashi, T. Yabuzaki

Published Oct 15, 2002• 25 citations
Publisher

Abstract

We observed broadband emission spectra of Cs-He excimers $({\mathrm{Cs}}^{*}\mathrm{He})$ in cold He gas $(1.3--100\mathrm{K}),$ when Cs atoms were excited to the $6{}^{2}P$ states. We calculated the emission spectrum from each vibrational state of ${\mathrm{Cs}}^{*}\mathrm{He}$ using Pascale's semiempirical Cs-He potential energy curves [J. Pascale, Phys. Rev. A $28,$ 632 (1983)], and compared the results with the observed spectra. From the measured spectral shape, we estimated the relative populations of the vibrational states of ${\mathrm{Cs}}^{*}\mathrm{He}$ at various He gas densities, and estimated the predissociation rate of ${\mathrm{Cs}}^{*}\mathrm{He}$ in the $A{}^{2}{\ensuremath{\Pi}}_{1/2}$ state. Moreover, a broadband emission spectrum of ${\mathrm{Cs}}^{*}{\mathrm{He}}_{2}$ was also observed, which was compared with that observed in liquid He.

DOI
10.1103/physreva.66.042505

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We observed broadband emission spectra of Cs-He excimers (Cs∗He)({\mathrm{Cs}}^{*}\mathrm{He})(Cs∗He) in cold He gas (1.3−−100K),(1.3--100\mathrm{K}),(1.3−−100K), when Cs atoms were excited to the 62P6{}^{2}P62P states. We calculated the emission spectrum from each vibrational state of Cs∗He{\mathrm{Cs}}^{*}\mathrm{He}Cs∗He using Pascale's semiempirical Cs-He potential energy curves [J. Pascale, Phys. Rev. A 28,28,28, 632 (1983)], and compared the results with the observed spectra. From the measured spectral shape, we estimated the relative populations of the vibrational states of Cs∗He{\mathrm{Cs}}^{*}\mathrm{He}Cs∗He at various He gas densities, and estimated the predissociation rate of Cs∗He{\mathrm{Cs}}^{*}\mathrm{He}Cs∗He in the A2\ensuremathΠ1/2A{}^{2}{\ensuremath{\Pi}}_{1/2}A2\ensuremathΠ1/2​ state. Moreover, a broadband emission spectrum of Cs∗He2{\mathrm{Cs}}^{*}{\mathrm{He}}_{2}Cs∗He2​ was also observed, which was compared with that observed in liquid He.
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​.
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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We present an experimental and theoretical study of the emission and absorption spectra of the Ba+{\mathrm{Ba}}^{+}Ba+ ions and Ba+∗He{\mathrm{Ba}}^{+*}\mathrm{He}Ba+∗He excimer quasimolecules in the cryogenic Ba-He plasma. We observe several spectral features in the emission spectrum, which we assign to the electronic transitions between bound states of the excimer correlating to the 62P3/26{\phantom{\rule{0.16em}{0ex}}}^{2}{P}_{3/2}62P3/2​ and 52D3/2,5/25{\phantom{\rule{0.16em}{0ex}}}^{2}{D}_{3/2,5/2}52D3/2,5/2​ states of Ba+{\mathrm{Ba}}^{+}Ba+. The resulting Ba+(52DJ)He{\mathrm{Ba}}^{+}(5{\phantom{\rule{0.16em}{0ex}}}^{2}{D}_{J})\text{He}Ba+(52DJ​)He is a metastable electronically excited complex with orbital angular momentum L=2L=2L=2, thus expanding the family of known metal-helium quasimolecules. It might be suitable for high-resolution spectroscopic studies and for the search for new polyatomic exciplex structures.
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