Coinage metal exciplexes with helium atoms: a theoretical study of M*(2L)Hen (M = Cu, Ag, Au; L = P,D)

Abstract

The structure and energetics of exciplexes M*((2)L)He(n) (M = Cu, Ag and Au; L = P and D) in their vibrational ground state are studied by employing diffusion Monte Carlo (DMC). Interaction potentials between the excited coinage metals and He atoms are built using the Diatomics-in-Molecule (DIM) approach and ab initio potential curves for the M((2)L)-He dimers. Extending our previous work [Cargnoni et al., J. Phys. Chem. A, 2011, 115, 7141], we computed the dimer potential for Au in the (2)P and (2)D states, as well for Cu and Ag in the (2)D state, employing basis set superposition error-corrected Configuration Interaction calculations. We found that the (2)Π potential correlating with the (2)P state of Au is substantially less binding than for Ag and Cu, a trend well supported by the M(+) ionic radiuses. Conversely, the interaction potentials between a (n - 1)d(9)ns(2 2)D metal and He present a very weak dependency on M itself or the projection of the angular momentum along the dimer axis. This is due to the screening exerted by the ns(2) electrons on the hole in the (n - 1)d shell. Including the spin-orbit coupling perturbatively in the DIM energy matrix has a major effect on the lowest potential energy surface of the (2)P manifold, the one for Cu allowing the formation of a "belt" of five He atoms while the one for Au being completely repulsive. Conversely, spin-orbit coupling has only a weak effect on the (2)D manifold due to the nearly degenerate nature of the diatomic potentials. Structural and energetic results from DMC have been used to support experimental indications for the formation of metastable exciplexes or the opening of non-radiative depopulation channels in bulk and cold gaseous He.

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

“…A similar behavior has been found for other species like copper, silver, and gold. 48−50 In contrast, states with y 7 P atomic limit (4 7 Σ + , 4 7 Π) and with y 5 P atomic limit (6 5 Σ + , 6 5 Π) show the typical shallow minimum as can be seen from Figure 4.…”

“…Considering the on-droplet states corresponding to the z 7 P and z 5 P states it seems possible that exciplexes can be formed by trapping He atoms in the deep potential minima. 50 …”

Dynamics of photoexcited Ba+ cations in 4He nanodroplets

“…Our method is equivalent to that of Ref. 46 in which the PESs are expressed as a function of the spherical coordinates angles.…”

Atomic collisions in suprafluid helium-nanodroplets: timescales for metal-cluster formation derived from He-density functional theory

“…Despite several theoretical studies of the interaction between a coinage metal dopant and the He environment, 18 , 19 information on He-mediated cluster formation processes for coinage metals is yet very scarce. Of particular interest to the community is the knowledge about timescales for cluster formation, since it is crucial for a controlled growth of nanoparticles in helium droplets.…”