Solvation and Spectral Line Shifts of Chromium Atoms in Helium Droplets Based on a Density Functional Theory Approach

Abstract

The interaction of an electronically excited, single chromium (Cr) atom with superfluid helium nanodroplets of various size (10 to 2000 helium (He) atoms) is studied with helium density functional theory. Solvation energies and pseudo-diatomic potential energy surfaces are determined for Cr in its ground state as well as in the y7P, a5S, and y5P excited states. The necessary Cr–He pair potentials are calculated by standard methods of molecular orbital-based electronic structure theory. In its electronic ground state the Cr atom is found to be fully submerged in the droplet. A solvation shell structure is derived from fluctuations in the radial helium density. Electronic excitations of an embedded Cr atom are simulated by confronting the relaxed helium density (ρHe), obtained for Cr in the ground state, with interaction pair potentials of excited states. The resulting energy shifts for the transitions z7P ← a7S, y7P ← a7S, z5P ← a5S, and y5P ← a5S are compared to recent fluorescence and photoionization experiments.

Photoinduced molecular dissociation and photoinduced recombination mediated by superfluid helium nanodroplets

“…8,9 An excess energy of about 0.4 eV (3200 cm À1 ), given by the difference of excitation energy and the dissociation limit (cf. 45) and is supported by the experimental observations, as follows. 1), can be compensated by the evaporation of 640 He atoms.…”

“…45 Surprisingly, we detect these three y 5 P 1;2;3 a 5 S 2 atom peaks not only at the Cr + ion mass, but also at Cr 2,3,4 + masses. The ionization spectra show, in addition to the droplet broadened molecular excitation structure, three pronounced peaks which we allocate to the y 5 P 1;2;3 a 5 S 2 Cr atomic transitions.…”

“…44,45 In principle, the atoms can remain solvated inside the He N , stay bound on the surface, or detach from the He N with a certain probability to take a few He atoms along. 44,45 In principle, the atoms can remain solvated inside the He N , stay bound on the surface, or detach from the He N with a certain probability to take a few He atoms along.…”

“…36 The Cr 2 + ion signal shows a clear dependence on the pick-up oven temperature. According to DFT calculations, 45 Cr* y 5 P1 atoms have a stable position on the surface and inside the He N , with a small energy barrier in between. .…”

Spatial quenching of a molecular charge-transfer process in a quantum fluid: the Csx–C60reaction in superfluid helium nanodroplets

“…A similar approach has been performed in the past e.g. for the explanation of spectra caused by electronic p-type excitations of heliophobic atoms residing on the droplet surface, 50 and it is a wellestablished method in the He-droplet community. [51][52][53][54][55][56] The average of both potentials in eqn (4) occurs due to the breaking of the cylindrical symmetry in the diatomic picture.…”