Spectroscopy and Dynamics of Al Atoms Solvated in Superfluid Helium Nanodroplets

Abstract

The laser-induced fluorescence excitation spectrum in the vicinity of the 32D ← 32P transition of Al atoms solvated in superfluid helium nanodroplets has been measured. While this transition has not been studied in bulk liquid helium, the observed blue shifts and line broadenings, compared with other transitions for which such measurements do exist, allow us to conclude that Al atoms reside in the interior of the helium droplet. The observed transition shows a splitting that we attribute to quadrupole-like deformations of the cavity formed in the helium droplet around the Al atom. Time-resolved studies of wavelength-selected emission from solvated Al atoms excited to the 32D state reveal a rapid (≤50 ps) and seemingly total nonradiative population transfer to the 42S state, the decay of which is found to account for all of the emission and to have a lifetime (6.4 ± 0.1 ns) that matches that of gas-phase Al.

Atomic and molecular defects in solid 4He

“…With the fine structure of the 3D state taken into account, this state splits into five M J components. As a consequence the absorption line profile calculated in [59] is composed of five overlapping components and has a spectral shift and a total width close to those of the experimental lineshape from [154]. The authors of [59] also reported a calculation of the absorption spectrum of the 3P − 4S transition that strongly underestimates the blueshift observed in experiment [125].…”

“…In Table 1 we list the elements studied up to date with the corresponding references. Also included in the table are the experiments by [151], [152] and [153,154] on He nano-droplets doped with Ag, Mg and Al atoms, since those atoms reside inside of the droplet and their observed spectra are very similar to those obtained in bulk liquid helium.…”

“…In the latter case, a splitting of the excited state may occur due to bubble oscillations. The experimental absorption spectrum of the 3P − 3D transition [154] reveals an asymmetric lineshape with two partially resolved components, separated by approximately 500 cm −1 . The authors of [154] suggest that an uncoupling of the spin-orbit interaction takes place and that a ring of 8 He atoms is formed around the waist of the dumbbell-like P z orbital -a structure similar to that of alkali-He exciplexes discussed below in Sec.…”

“…23 and Table 2. Time-resolved fluorescence of atoms embedded in liquid He was reported in [125,120,94] for bulk liquid and in [153,154] for He nano-droplets. The Cs 6P 1/2 lifetime was found [94] to be pressure independent up to the solidification point, with a value slightly below the free atomic lifetime, while the lifetime of the corresponding 5P 1/2 state of Rb decreasd with increasing pressure, leading to a complete quenching of the fluorescence.…”

Spectroscopy and dynamics in helium nanodroplets

“…Higher temperatures are often used to establish the required vapor pressure from bulk material inside a heated cell. Temperatures exceeding 1500 K have been used in order to evaporate metals [36]. Thermal radiation from the cell or heating are not a problem for the droplet beam because dipole active transitions in helium require 20 eV of photon energy.…”