Emission spectra of Cs-He excimers in cold helium gas

Abstract

We observed broadband emission spectra of Cs-He excimers (Cs*He) in cold He gas (1.3-100 K), when Cs atoms were excited to the 6 2 P 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 ͑1983͔͒, 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 ⌸ 1/2 state. Moreover, a broadband emission spectrum of Cs*He 2 was also observed, which was compared with that observed in liquid He.

Cs * He n exciplexes in solid He4

“…The formation of alkali-helium exciplexes was considered for the first time by Dupont-Roc [1] and Kanorsky et al [2] as an explanation for the observed quenching of atomic fluorescence from light alkali atoms (Na, Li) embedded in liquid and solid 4 He. In the meantime such exciplex molecules have been observed in liquid helium and in cold helium gas [3][4][5], as well as on the surface of helium nanodroplets [6][7][8][9]. In this paper we present a theoretical and experimental study of cesium-helium exciplexes formed in a solid helium matrix, and give a more detail account on our recent observation [10] of these complexes.…”

“…For cesium, however, the exciplex with three helium atoms is unstable and therefore its formation and hence the subsequent formation of larger exciplexes was expected to be suppressed. Experiments in cold helium gas, in which the relatively low collision rate justifies an analysis in terms of sequential capture processes, have indeed shown [3] that only Cs * He 1 and Cs * He 2 exciplexes are formed, with no evidence for complexes with n > 2.…”

“…Our modelling of the structure and emission spectra of Cs * He n exciplexes follows the approach of [3,4]. As the emission spectra are mainly determined by the n bound helium atoms we consider only the influence of those atoms and neglect the influence of the bulk of the surrounding helium matrix.…”

“…A detailed comparative analysis of Cs * He n=1,2 and Rb * He n=1...6 exciplexes was performed by the Kyoto group [3,4]. The authors have considered the formation of the exciplexes as a sequential process, in which helium atoms are attached to the complex one by one.…”

Spectroscopy of alkali-metal atoms in dense supercritical4He at low temperatures

“…These quasimolecular structures arising from the highly anisotropic alkali-metal-helium interaction have been analyzed in detail in [25,[38][39][40][41]. The dependence of the exciplex populations on He temperature and density in the range of ρ 0 = 10 18 -10 19 cm −3 was studied experimentally in [38,42]. Neglecting the population of the exciplex states, especially those in the B 3/2 electronic state, leads mainly to a discrepancy between the experimental and calculated spectra in the range of 930-980 nm (see Fig.…”