Photodepletion probes of Na5, Na6, and Na7. Molecular dimensionality transition (2D→3D)?

Abstract

Photodepletion spectroscopy was used to obtain electronic absorption data for Na5, Na6, and Na7 in a wavelength range from 420–770 nm. Measurements were rationalized using several models, ranging from classical electrostatic to ab initio large-scale configuration-interaction calculations. As in previous studies of Na4, Na8, and Na20, classical Mie–Drude theory applied to appropriately dimensioned metal droplets describes the gross but not a number of fine-structure features of the spectra observed. In contrast, ab initio large-scale configuration-interaction predictions of vertical electronic excitations from specific ground-state geometries can more fully account for the measurements. Theory–experiment comparison suggests that Na6 is predominantly formed under our molecular-beam conditions in a planar or near-planar structure. In contrast, the spectrum obtained for Na7 is consistent with a three-dimensional topology.

Photoabsorption in sodium clusters on the basis of time-dependent density-functional theory

“…[9][10][11]25,52 In total, we have found an excellent agreement with the experimental obtained absorption spectra of Wang and co-workers. 12,13 The spectra also match well with those of Bonačić-Koutecký and co-workers [16][17][18] and others. The influence of the geometry with respect to position and intensity of the absorption peaks is of crucial importance.…”

“…͑5͒ The first major excitation peaks occur in an energy range between 2 and 3 eV for nearly all displayed spectra. ͑6͒ The spectrum of Na 13 shows an exceptional intensity of a single absorption peak at 2.6 eV, which is double as high as any peak in the other displayed spectra.…”

“…For Na 5 , the experimental data 13 are not as clear as for the other clusters. The main absorption band is centered around 605 nm ͑2.05 eV͒.…”

“…For the clusters with three to eight atoms the experimental spectra have been measured by Wang and co-workers. 12,13 In case of the Na 3 cluster ͓Fig. 3͑a͔͒ we found absorption peaks in the energy range that has been scanned in the experiment ͑1.48-3.35 eV͒.…”

“…These studies resulted in size-dependent absorption cross sections at fixed absorption energies. [9][10][11] Wang and co-workers 12,13 obtained the absorption spectra by photodepletion spectroscopy. These spectra have been recorded for small size-selected neutral Na clusters with less than ten atoms and cover the energy range of approximately 1.5-3.0 eV.…”