Alkaline earth metals (Ca, Sr) attached to liquid helium droplets: Inside or out?

The structure of small mixed helium clusters doped with one calcium atom has been determined within the diffusion Monte Carlo framework. The results show that the calcium atom sits at the 4 He-3 He interface. This is in agreement with previous studies, both experimental and theoretical, performed for large clusters. A comparison between the results obtained for the largest cluster we have considered for each isotope shows a clear tendency of the Ca atom to reside in a deep dimple at the surface of the cluster for 4 He clusters, and to become fully solvated for 3 He clusters. We have calculated the absorption spectrum of Ca around the 4s4p ← 4s 2 transition and have found that it is blue-shifted from that of the free-atom transition by an amount that depends on the size and composition of the cluster.

Section: Discussionsupporting

confidence: 76%

“…A similar peak appears in the experiments, and it is due to the excitation of gas-phase Ca atoms present in the doping chamber [47].…”

Section: Resultsmentioning

confidence: 60%

Ca impurity in small mixed H4e–H3e clusters

Guardiola

Navarro

Mateo

et al. 2009

“…and from the geometrical center of the cluster Figure 4 and 5 display the results for R(r) respect to the geometrical center; these are normalized such that ∞ 0 R(r) He r 2 dr = N He (14) for the helium atoms, while…”

Section: Resultsmentioning

confidence: 99%

“…Moreover, the low temperature of these clusters can help spectroscopic studies on large molecules: the electronic spectra of the aminoacids tryptophan and tyrosine were simplified by cooling their vibrational motion inside an 4 He droplet [13], llowing an easier interpretation of the experimental results. While alkali and alkali-earth atoms are adsorbed on 4 He clusters and then investigated by electronic spectra [14,15], all other impurities, studied by means of infra-red spectroscopy, reside inside the clusters themselves [6,12], and strongly perturbate their structure and properties. This difference is due to the weaker or stronger interactions between the helium atom and the doping molecule than between two helium atoms.…”

Section: Introductionmentioning

confidence: 99%

Quantum Monte Carlo study of the H− impurity in small helium clusters

Casalegno

Mella

Morosi

et al. 2000

We report ground state energies and structural properties for small helium clusters ( 4 He) containing an H − impurity computed by means of variational and diffusion Monte Carlo methods. Except for 4 He2H − that has a noticeable contribution from collinear geometries where the H − impurity lies between the two 4 He atoms, our results show that our 4 HeN H − clusters have a compact 4 HeN subsystem that binds the H − impurity on its surface. The results for N ≥ 3 can be interpreted invoking the different features of the minima of the He-He and He-H − interaction potentials.

“…However, they stressed that no clear cut description of this system could be recovered by theory using the model proposed by Ancillotto et al [5] because the λ values computed from the available model potentials for Mg-He are heavily scattered around the critical value of 1.9 (see Refs. [15] and [16], and Ref. [14] for an exhaustive review up to 1999); furthermore, the performance of this scheme in nearly critical conditions (i.e.…”

Section: Introductionmentioning

confidence: 99%

Predicting atomic dopant solvation in helium clusters: The MgHen case

Mella

Calderoni

Cargnoni

2005

We present a quantum Monte Carlo study of the solvation and spectroscopic properties of the Mg doped helium clusters MgHen with n = 2 − 50. Three high level (MP4, CCSD(T) and CCSDT) MgHe interaction potentials have been used to study the sensitivity of the dopant location on the shape of the pair interaction. Despite the similar MgHe well depth, the pair distribution functions obtained in the diffusion Monte Carlo simulations markedly differ for the three pair potentials, therefore indicating different solubility properties for Mg in Hen. Moreover, we found interesting size effects for the behavior of the Mg impurity.As a sensitive probe of the solvation properties, the Mg excitation spectra have been simulated for various cluster sizes and compared with the available experimental results. The interaction between the excited 1 P Mg atom and the He moiety has been approximated using the Diatomics-in-Molecules method and the two excited 1 Π and 1 Σ MgHe potentials. The shape of the simulated MgHe50 spectra show a substantial dependency on the location of the Mg impurity, and hence on the MgHe pair interaction employed.To unravel the dependency of the solvation behavior on the shape of the computed potentials, exact Density Functional Theory has been adapted to the case of doped Hen and various energy distributions have been computed. The results indicate the shape of the repulsive part of the MgHe potential as an important cause of the different behaviours.