Investigations of the Optical Spectroscopy of Atomic Sodium Isolated in Solid Argon and Krypton: Experiments and Simulations.

Abstract

The absorption spectra of thin film samples, formed by the codeposition of sodium vapor with the rare gases have long been known to consist of complex structures in the region of the atomic sodium "yellow-doublet" lines. The photophysical characteristics of the associated luminescence (excitation/emission) spectra, indicate strong interaction between the excited P state Na atom and the rare gases (Ar, Kr, and Xe) used as host solids. This system is reinvestigated with new experimental spectroscopic results and molecular dynamics (MD) calculations. The so-called "violet" site in Ar and Kr has been produced by laser excitation of thermally deposited samples. The simulation of the "spray-on" deposition of thin films enables identification of tetravacancy (tv) sites of isolation for ground-state atomic sodium in Ar while in Kr this site is found in addition to single vacancy (sv) occupancy. Various cubic symmetry sites were taken into account to simulate absorption and emission spectra using accurate interaction potentials for the Na · RG diatomics. The wellknown 3-fold splitting in absorption, attributed to the Jahn-Teller effect, was very well reproduced but the simulated spectra for all the sites considered are located in the low energy region of the experimental bands. The evolution of the excited state Na atom is followed revealing the nature and symmetry of the sites that are transiently occupied. Consistent with the large Stokes shift observed experimentally, there is an extensive rearrangement of the lattice in the excited state with respect to the ground state. Combining all the experimental and theoretical information, an assignment of experimental violet, blue, and red absorption features is established involving single vacancy, tetravacancy, and hexavacancy sites, respectively, in Ar and Kr.

Luminescence spectroscopy of matrix-isolated atomic manganese: Site size and orbital occupancy dependence of crystal field splitting

“…The bond length predictions indicate strong similarities between the Mn· RG and Mg· RG systems and dissimilarities with the Na· RG system. Thus occupancy of metal atoms in smaller sites will be favored in the Mn/RG systems compared to what has been found in MD calculations 12 of the site occupancy in the Na/RG systems.…”

“…Based on Na/RG molecular dynamics calculations, 12 the red absorption bands in Ar and Kr are attributed to larger TV sites. In summary, the blue site y 6 P state absorption/excitation bands in Ar, Kr, and Xe are attributed to SV site occupancy, while the red sites in Ar and Kr are ascribed to TV sites.…”

“…Contrary to expectation, it was established that certain sites are capable of considerable broadening on d → s transitions while others exhibit the normal characteristics of narrow and unshifted emission from the gas phase position. In a recent molecular dynamics study of matrix-isolated atomic sodium 12 the nature of the sites occupied by this large atom was examined. As anticipated, large tetravacancy ͑TV͒ and hexavacancy sites were found in simulated depositions for Na in Ar and Kr.…”

Metal atom (Zn, Cd and Mg) luminescence in solid neon

“…It might be further proposed that the blue, threecomponent feature of Zn/Ne, centered at 204.5 nm, and the corresponding Cd/Ne feature centered at 219, arise from occupancy in a more compact tetra-vacancy site. Molecular dynamics calculations, such as those conducted on the matrix-isolated alkali metal atoms [29], are required to examine these site occupancy proposals.…”

Potential energy curves and spin-orbit coupling of light alkali-heavy rare gas molecules

“…This relative simplicity is particularly convenient to investigate more complex situations when the M is coupled to additional rare gas atoms at the surface of RG clusters, or trapped in RG matrices, and to unravel the fine details of the guest-hosts interaction. Models based either on diatomics-inmolecules [1][2][3] or on core polarization potential (CPP) 4,5 have been used to investigate these more complex situations. In both cases, reliable potential energy curves (PEC) for dimers are necessary to parameterize or to assess the quality of the models.…”