Electronically excited rubidium atom in helium clusters and films. II. Second excited state and absorption spectrum

Abstract

Following our work on the study of helium droplets and film doped with one electronically excited rubidium atom Rb(∗) ((2)P) [M. Leino, A. Viel, and R. E. Zillich, J. Chem. Phys. 129, 184308 (2008)], we focus in this paper on the second excited state. We present theoretical studies of such droplets and films using quantum Monte Carlo approaches. Diffusion and path integral Monte Carlo algorithms combined with a diatomics-in-molecule scheme to model the nonpair additive potential energy surface are used to investigate the energetics and the structure of Rb(∗)He(n) clusters. Helium films as a model for the limit of large clusters are also considered. As in our work on the first electronic excited state, our present calculations find stable Rb(∗)He(n) clusters. The structures obtained are however different with a He-Rb(∗)-He exciplex core to which more helium atoms are weakly attached, preferentially on one end of the core exciplex. The electronic absorption spectrum is also presented for increasing cluster sizes as well as for the film.

Photoionisaton of pure and doped helium nanodroplets

“…AkHe association can only occur by a tunneling process. Subsequent desorption of the AkHe exciplex is driven by repulsive forces acting between the exciplex and the whole droplet and possibly by vibrational relaxation of the AkHe molecule which induced its evaporation off droplet surface [77]. On the other hand, higher-lying Ak states often feature extended attractive wells in the AkHe pair-potentials.…”

“…Although different formation mechanisms have been ascertained (direct association vs. tunneling), a detailed description is still evolving [77,141]. So is the dynamics of the collapse of a foam-like structure of magnesium atoms formed by aggregation inside He droplets when being irradiated by ultrashort light pulses [109].…”

“…In spite of the repulsion of excited Ak atoms from He droplets for most of the excited states, pair-wise attraction between Ak * and individual He atoms can induce the formation of Ak * He n , n = 1, 2, 3 exciplexes as a competing process to desorption of Ak * off the droplet surface. While the equilibrium properties of Ak * He exciplexes are now well characterized even including an environment given by a He cluster or film [77], the dynamics of the formation process of Ak * He exciplexes still eludes from an accurate description [70,71,74]. The dynamics of the formation of sodium (Na) and potassium (K) exciplexes (Na * He, K * He) has first been studied by time-resolved fluorescence emission spectroscopy, yielding formation times in the range of tens of ps [76].…”

“…The fast modulation of the data results from quantum interference and contains information about the REMPI spectrum in the spectral range which falls into of bandwidth of the fs laser [71]. Theoretical models including one-dimensional semiclassical tunneling [76], quantum-classical modeling [147], semiclassical path integral molecular dynamics [148], and quantum Monte Carlo approaches [77] have predicted values for the exciplex formation times ranging from 1.7 ps for the lithium-He exciplex Li*He, to 31 ps for Rb*He in the 1 2 Π 3/2 -state. The role of the superfluid properties of He on the exciplex formation times has been directly probed in experiments with 3 He droplets [70].…”

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].…”