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−−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+ 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
15K.
We report the observation of emission spectra from
Rb∗Hen exciplexes in solid
4He. Two different excitation channels were experimentally identified, viz., exciplex formation via laser excitation to the atomic
5P3∕2 and to the
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
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 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 report on the systematic observation of emission spectra of
Rb∗Hen exciplexes
(n=1,2,…,6), realized by exciting Rb atoms to the
52P states
(Rb∗) in a cold
4He gas. The observed broad spectral components are assigned to
Rb∗Hen (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 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.We observed broadband emission spectra of Cs-He excimers
(Cs∗He) in cold He gas
(1.3−−100K), when Cs atoms were excited to the
62P states. We calculated the emission spectrum from each vibrational state of
Cs∗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
Cs∗He at various He gas densities, and estimated the predissociation rate of
Cs∗He in the $A{}^{2}{\ensuremath{\Pi}}_{1/2}$ state. Moreover, a broadband emission spectrum of
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 exciplexes
(n=1,2,…,6), realized by exciting Rb atoms to the
52P states
(Rb∗) in a cold
4He gas. The observed broad spectral components are assigned to
Rb∗Hen (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 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.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−−25K. We have observed laser-induced fluorescence spectra of
Ba+ and ${\mathrm{Ba}}^{+*}\text{\ensuremath{-}}\mathrm{He}$ exciplexes by means of
D2 excitation of
Ba+ ions. Using the rate equation analyses of fluorescence intensities of ${\mathrm{Ba}}^{+*}\text{\ensuremath{-}}\mathrm{He}$ and
Ba+, we have determined the rate constant of exciplex formation (
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
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
15K. 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 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
3.6K. In cold He gas at
25K or lower, a new channel of population transfer from the
6p 2P3∕2 state to the
6p 2P1∕2 state of
Ba+ is opened because both exciplex formation and dissociation start to occur frequently.