Spectroscopy of Mg atoms solvated in helium nanodroplets

Abstract

We have measured the laser-induced fluorescence excitation spectra of the 3 1P10←3 1S0 transition of Mg atoms solvated in helium nanodroplets. The observed blue shifts and line broadenings mirror the shifts and broadenings observed in studies of Mg atoms solvated in bulk liquid helium. This similarity allows us to conclude that Mg atoms reside in the interior of the helium droplet. The 3 1P10←3 1S0 transition shows a splitting which we attribute to a quadrupolelike deformation of the cavity which forms around the solute atom after excitation. Temporal evolution of the fluorescence from the solvated 3 1P10 Mg yields a longer lifetime (2.39±0.05 ns) than found in vacuum (1.99±0.08 ns). This difference can be accounted for quantitatively by evaluation of the anisotropic distribution of the helium density in the neighborhood of the excited Mg atom. The question of solvation vs surface location for the guest atoms is also discussed in light of the model of Ancilotto et al. [F. Ancilotto, P. B. Lerner, and M. W. Cole, J. Low Temp. Phys. 101, 1123 (1995)], of existing metal atom–helium potential energy functions, and of our own calculations for the MgHe and CaHe ground states. While the Ancilotto model successfully predicts solvation (or lack of it) if the solvation parameter of the guest atom is not too near the threshold of 1.9, the present knowledge of the interatomic potentials is not precise enough to test the model in the neighborhood of the critical value.

Predicting atomic dopant solvation in helium clusters: The MgHen case

“…In Section III we give a short introduction to the quantum Monte Carlo methods used in this work to solve the Schrödinger equation for nuclear motion. In Section IV we present the results of the DMC simulations, and compare our data with the available experimental measurements [13,14]. Finally, Section V reports our conclusions, along with a prospect on future applications.…”

“…In the case of the ground state Mg-He complex, a number of interaction energy curves were proposed in the last fifteen years [14,16,17,20,21,22,23]. The most accurate were computed by Funk et al [21], Partridge et al [16], and by Hinde [17].…”

“…Moriwaki et al [13] measured the emission and the excitation spectra of Mg dispersed in liquid helium by means of ultraviolet laser excitation, and focused their attention on the signals arising from the Mg(3s 2 ) 1 S→Mg(3s3p) 1 P transition. Reho et al [14] studied this same transition of Mg while interacting with helium nanodroplets. Based on the comparison with the available experimental data for Mg [13] and for other neutral metal atoms in helium, Reho et al concluded that Mg is indeed solvated by helium, and thus does not reside on the surface of the nanodroplets.…”

“…In the present study we applied this method to study the doping of helium clusters with a neutral Mg atom, a system that in recent years has been the subject of two experimental investigations [13,14]. Moriwaki et al [13] measured the emission and the excitation spectra of Mg dispersed in liquid helium by means of ultraviolet laser excitation, and focused their attention on the signals arising from the Mg(3s 2 ) 1 S→Mg(3s3p) 1 P transition.…”

“…[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. for λ values close to 1.9) still needed to be assessed.…”