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Physical Review A

Emission spectra of (RbHen)-He-* exciplexes in a cold He-4 gas

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

Published Jul 1, 2003• 0 citations
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Abstract

We report on the systematic observation of emission spectra of ${\mathrm{Rb}}^{*}{\mathrm{He}}_{n}$ exciplexes $(n=1,2,\dots{},6),$ realized by exciting Rb atoms to the ${5}^{2}P$ states $({\mathrm{Rb}}^{*})$ in a cold ${}^{4}\mathrm{He}$ gas. The observed broad spectral components are assigned to ${\mathrm{Rb}}^{*}{\mathrm{He}}_{n}$ $(n=1--6)$ 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 ${\mathrm{Rb}}^{*}\mathrm{He}$ 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 ${\mathrm{Rb}}^{*}{\mathrm{He}}_{6}.$

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Keiichi Hirano, Katsunari Enomoto, M. Kumakura +2 more

We report on the systematic observation of emission spectra of ${\mathrm{Rb}}^{*}{\mathrm{He}}_{n}$ exciplexes $(n=1,2,\dots{},6),$ realized by exciting Rb atoms to the ${5}^{2}P$ states $({\mathrm{Rb}}^{*})$ in a cold ${}^{4}\mathrm{He}$ gas. The observed broad spectral components are assigned to ${\mathrm{Rb}}^{*}{\mathrm{He}}_{n}$ $(n=1--6)$ 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 ${\mathrm{Rb}}^{*}\mathrm{He}$ 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 ${\mathrm{Rb}}^{*}{\mathrm{He}}_{6}.$

Physical Review A•Jul 25, 2003•39 citations

Rb*Hen exciplexes in solid He4

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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.

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Emission spectra of Cs-He excimers in cold helium gas

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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.

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Laser-induced fluorescence spectra of Ba+*-He exciplexes produced in cold He gas

Yoshimitsu Fukuyama, Yoshiki Moriwaki, Yukari Matsuo

We report the observation of laser-induced fluorescence spectra of ${\text{Ba}}^{+*}\text{\ensuremath{-}}\text{He}$ exciplexes. The experiment is carried out in an environment of cold gaseous helium at a temperature range of $3--30\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. We have observed the emission spectra of exciplexes by means of excitation of the $6p\phantom{\rule{0.3em}{0ex}}^{2}P_{3∕2}\ensuremath{\leftarrow}6s\phantom{\rule{0.3em}{0ex}}^{2}S_{1∕2}$ transition of ${\text{Ba}}^{+}$ ions. It is found that these spectra are redshifted from the $D2$ emission line in the free space and are composed of several peaks. The experimental results are reproduced well by theoretical calculation of the emission spectra for vibrational levels of ${\text{Ba}}^{+*}\text{\ensuremath{-}}\text{He}$. We also investigate the vibrational dynamics of the $6p\phantom{\rule{0.3em}{0ex}}^{2}\ensuremath{\Pi}_{3∕2}$ state of ${\text{Ba}}^{+*}\text{\ensuremath{-}}\text{He}$, and we have determined the collision-induced vibrational relaxation cross sections of the $6p\phantom{\rule{0.3em}{0ex}}^{2}\ensuremath{\Pi}_{3∕2}$ state to be $9.7\ifmmode\pm\else\textpm\fi{}1.1\phantom{\rule{0.3em}{0ex}}{\mathrm{\AA{}}}^{2}$ at $15\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.

Physical Review A•Apr 7, 2004•15 citations

Condensation of He Gas on Optically Excited Ag Atoms Below the Critical Temperature ( T<5.2K )

Zygmunt J. Jakubek, Qin Hui, Michio Takami

Laser induced fluorescence spectra of Ag atoms and their time profiles have been studied in cold He gas at temperatures 4.3--25 K and pressure $\ensuremath{\lesssim}1\mathrm{atm}$. The emission spectra following the excitation of the atomic $D2$ line consist of three narrow lines and three broadbands, which are assigned to transitions of Ag atoms and AgHe and ${\mathrm{AgHe}}_{2}$ exciplexes. Surprisingly long ( $\ensuremath{\gtrsim}300\mathrm{ns}$) effective emission lifetimes are observed at $T>{T}_{c}$ (5.2 K). The long lifetimes are the result of population trapping in the ${}^{2}{D}_{5/2}$ metastable state. At $T\ensuremath{\lesssim}{T}_{c}$, the effective lifetimes decrease to $\ensuremath{\lesssim}20\mathrm{ns}$ due to the condensation of He gas on the Ag atom in its ${}^{2}{D}_{5/2}$ state.

Physical Review Letters•Jul 28, 1997•30 citations

Formation and dissociation of Ba+*−He exciplexes at 3–25K

Yoshimitsu Fukuyama, Yoshiki Moriwaki, Yukari Matsuo

We report the formation rate constants and the dissociation cross sections of ${\mathrm{Ba}}^{+*}\text{\ensuremath{-}}\mathrm{He}$ exciplexes in an environment of cold gaseous helium at temperatures of $3--25\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. We have observed laser-induced fluorescence spectra of ${\mathrm{Ba}}^{+}$ and ${\mathrm{Ba}}^{+*}\text{\ensuremath{-}}\mathrm{He}$ exciplexes by means of $D2$ excitation of ${\mathrm{Ba}}^{+}$ ions. Using the rate equation analyses of fluorescence intensities of ${\mathrm{Ba}}^{+*}\text{\ensuremath{-}}\mathrm{He}$ and ${\mathrm{Ba}}^{+}$, we have determined the rate constant of exciplex formation (${\mathrm{Ba}}^{+}$: $6p$ $^{2}P_{3∕2}+2\mathrm{He}\ensuremath{\rightarrow}{\mathrm{Ba}}^{+*}\text{\ensuremath{-}}\mathrm{He}$: $6p$ $^{2}\ensuremath{\Pi}_{3∕2}+\mathrm{He}$) attributable to three-body collision at 5, 10, 15, and $20\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The formation rate constant was found to have irregular temperature dependence, with a local maximum ${k}_{f}=(6.0\ifmmode\pm\else\textpm\fi{}0.8)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}44}\phantom{\rule{0.3em}{0ex}}{\mathrm{m}}^{6}\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ at $15\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Results of this study also indicate peculiar temperature dependence of the dissociation cross section (${\mathrm{Ba}}^{+*}\text{\ensuremath{-}}\mathrm{He}$: $6p$ $^{2}\ensuremath{\Pi}_{3∕2}\ensuremath{\rightarrow}{\mathrm{Ba}}^{+}$: $6p$ $^{2}P_{1∕2}+\mathrm{He}$). It has a local maximum ${\ensuremath{\sigma}}_{\mathrm{dis}}=(3.1\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}21}\phantom{\rule{0.3em}{0ex}}{\mathrm{m}}^{2}$ at $3.6\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. In cold He gas at $25\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ or lower, a new channel of population transfer from the $6p$ $^{2}P_{3∕2}$ state to the $6p$ $^{2}P_{1∕2}$ state of ${\mathrm{Ba}}^{+}$ is opened because both exciplex formation and dissociation start to occur frequently.

Physical Review A•Mar 30, 2007•7 citations
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​.
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 $\mathrm{Rb}\text{\ensuremath{-}}\mathrm{He}$ and $\mathrm{Cs}\text{\ensuremath{-}}\mathrm{He}$ systems.
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 $A{}^{2}{\ensuremath{\Pi}}_{1/2}$ 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 the observation of laser-induced fluorescence spectra of ${\text{Ba}}^{+*}\text{\ensuremath{-}}\text{He}$ exciplexes. The experiment is carried out in an environment of cold gaseous helium at a temperature range of 3−−30K3--30\phantom{\rule{0.3em}{0ex}}\mathrm{K}3−−30K. We have observed the emission spectra of exciplexes by means of excitation of the $6p\phantom{\rule{0.3em}{0ex}}^{2}P_{3∕2}\ensuremath{\leftarrow}6s\phantom{\rule{0.3em}{0ex}}^{2}S_{1∕2}$ transition of Ba+{\text{Ba}}^{+}Ba+ ions. It is found that these spectra are redshifted from the D2D2D2 emission line in the free space and are composed of several peaks. The experimental results are reproduced well by theoretical calculation of the emission spectra for vibrational levels of ${\text{Ba}}^{+*}\text{\ensuremath{-}}\text{He}$. We also investigate the vibrational dynamics of the $6p\phantom{\rule{0.3em}{0ex}}^{2}\ensuremath{\Pi}_{3∕2}$ state of ${\text{Ba}}^{+*}\text{\ensuremath{-}}\text{He}$, and we have determined the collision-induced vibrational relaxation cross sections of the $6p\phantom{\rule{0.3em}{0ex}}^{2}\ensuremath{\Pi}_{3∕2}$ state to be $9.7\ifmmode\pm\else\textpm\fi{}1.1\phantom{\rule{0.3em}{0ex}}{\mathrm{\AA{}}}^{2}$ at 15K15\phantom{\rule{0.3em}{0ex}}\mathrm{K}15K.
Laser induced fluorescence spectra of Ag atoms and their time profiles have been studied in cold He gas at temperatures 4.3--25 K and pressure $\ensuremath{\lesssim}1\mathrm{atm}$. The emission spectra following the excitation of the atomic D2D2D2 line consist of three narrow lines and three broadbands, which are assigned to transitions of Ag atoms and AgHe and AgHe2{\mathrm{AgHe}}_{2}AgHe2​ exciplexes. Surprisingly long ( $\ensuremath{\gtrsim}300\mathrm{ns}$) effective emission lifetimes are observed at T>TcT>{T}_{c}T>Tc​ (5.2 K). The long lifetimes are the result of population trapping in the 2D5/2{}^{2}{D}_{5/2}2D5/2​ metastable state. At $T\ensuremath{\lesssim}{T}_{c}$, the effective lifetimes decrease to $\ensuremath{\lesssim}20\mathrm{ns}$ due to the condensation of He gas on the Ag atom in its 2D5/2{}^{2}{D}_{5/2}2D5/2​ state.
We report the formation rate constants and the dissociation cross sections of ${\mathrm{Ba}}^{+*}\text{\ensuremath{-}}\mathrm{He}$ exciplexes in an environment of cold gaseous helium at temperatures of 3−−25K3--25\phantom{\rule{0.3em}{0ex}}\mathrm{K}3−−25K. We have observed laser-induced fluorescence spectra of Ba+{\mathrm{Ba}}^{+}Ba+ and ${\mathrm{Ba}}^{+*}\text{\ensuremath{-}}\mathrm{He}$ exciplexes by means of D2D2D2 excitation of Ba+{\mathrm{Ba}}^{+}Ba+ ions. Using the rate equation analyses of fluorescence intensities of ${\mathrm{Ba}}^{+*}\text{\ensuremath{-}}\mathrm{He}$ and Ba+{\mathrm{Ba}}^{+}Ba+, we have determined the rate constant of exciplex formation (Ba+{\mathrm{Ba}}^{+}Ba+: 6p6p6p $^{2}P_{3∕2}+2\mathrm{He}\ensuremath{\rightarrow}{\mathrm{Ba}}^{+*}\text{\ensuremath{-}}\mathrm{He}$: 6p6p6p $^{2}\ensuremath{\Pi}_{3∕2}+\mathrm{He}$) attributable to three-body collision at 5, 10, 15, and 20K20\phantom{\rule{0.3em}{0ex}}\mathrm{K}20K. The formation rate constant was found to have irregular temperature dependence, with a local maximum ${k}_{f}=(6.0\ifmmode\pm\else\textpm\fi{}0.8)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}44}\phantom{\rule{0.3em}{0ex}}{\mathrm{m}}^{6}\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ at 15K15\phantom{\rule{0.3em}{0ex}}\mathrm{K}15K. Results of this study also indicate peculiar temperature dependence of the dissociation cross section (${\mathrm{Ba}}^{+*}\text{\ensuremath{-}}\mathrm{He}$: 6p6p6p $^{2}\ensuremath{\Pi}_{3∕2}\ensuremath{\rightarrow}{\mathrm{Ba}}^{+}$: 6p6p6p 2P1∕2+He^{2}P_{1∕2}+\mathrm{He}2P1∕2​+He). It has a local maximum ${\ensuremath{\sigma}}_{\mathrm{dis}}=(3.1\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}21}\phantom{\rule{0.3em}{0ex}}{\mathrm{m}}^{2}$ at 3.6K3.6\phantom{\rule{0.3em}{0ex}}\mathrm{K}3.6K. In cold He gas at 25K25\phantom{\rule{0.3em}{0ex}}\mathrm{K}25K or lower, a new channel of population transfer from the 6p6p6p 2P3∕2^{2}P_{3∕2}2P3∕2​ state to the 6p6p6p 2P1∕2^{2}P_{1∕2}2P1∕2​ state of Ba+{\mathrm{Ba}}^{+}Ba+ is opened because both exciplex formation and dissociation start to occur frequently.