Spectroscopy of alkali atoms (Li, Na, K) attached to large helium clusters

Abstract

Large liquid helium clusters (He L , n+10) produced in a supersonic jet are doped with alkali atoms (Li, Na, K) and characterized by means of laser induced fluorescence. Each cluster contains, on average, less than one dopant atom. Both excitation and emission spectra have been recorded. The observed excitation spectra are analyzed, calculating the transitions within an approach based on the hypothesis that the chromophores are trapped in a dimple on the cluster's surface as predicted by the theoretical calculations of Ancilotto et al. [9]. The results of the model calculations are in good qualitative agreement with the experimental findings. In spite of the very weak binding energy (a few cm\), some of the excited atoms remain bound to the surface, provided the excitation occurs at frequencies not too far from the alkali's gas phase absorptions. These bound-bound excitations produce very broad, red shifted emission spectra. At other, blue shifted frequencies, the excited atoms desorb from the cluster's surface, giving rise to unshifted, free atom, emission spectra. The heavier alkali metals (Na, K) show, compared to the calculations, an additional broadening which is attributed to surface excitations on the helium droplet.

Rotational and vibrational dynamics of CO2 and N2O in helium nanodroplets

“…It has been experimentally determined that alkali atoms reside at the surface of 4 He droplets [56,59], a result that is reproduced by DFT calculations [56]. At variance, Rb + and Cs + cations are fully solvated and develop snowball structures [3].…”

Spectroscopy and dynamics in helium nanodroplets

“…In several studies the formation of alkali-helium exciplexes upon excitation of atomic transitions explained the observed features in wavelength dispersed, laser- induced fluorescence spectra [59,166,60,167,165]. Fig.…”

Dynamics of solvation and desolvation of rubidium attached to He nanodroplets

“…studied using nanosecond pulsed excitation and velocitymap imaging of photoions and electrons [14,16]. Due to the interaction of the excited Rb atom with the He droplet surface, the 6p-state splits up into the two states 6pΣ and 6pΠ according to the pseudo-diatomic model which treats the whole He droplet, He N , as one constituent atom of the RbHe N complex [23,34,35]. Using the RbHe N pseudo-diatomic potential curves for the 5sΣ electronic groundstate and the 6pΣ, Π excited states we compute the Franck-Condon profiles for the expected vertical excitation probability using R. LeRoy's program BCONT [38].…”