| Sumario: | Photoelectron spectroscopy has been conducted for a series of (CrO) (n = 1-5) clusters and compared with density functional calculations. Well-resolved photoelectron spectra were obtained for (CrO) (n = 1-5) at 193 nm (6.424 eV) and 157 nm (7.866 eV) photon energies, allowing for accurate measurements of the electron binding energies, low-lying electronic excitations for n = 1 and 2, and the energy gaps. Density functional and molecular orbital theory (CCSD(T)) calculations were performed to locate the ground and low-lying excited states for the neutral clusters and to calculate the electron binding energies of the anionic species. The experimental and computational studies firmly establish the unique low-spin, nonplanar, cyclic ring structures for (CrO) and (CrO) for n ≥ 3. The structural parameters of (CrO) are shown to converge rapidly to those of the bulk CrO crystal. The extra electron in (CrO) (n ≥ 2) is shown to be largely delocalized over all Cr centers, in accord with the relatively sharp ground-state photoelectron bands. The measured energy gaps of (CrO) exhibit a sharp increase from n = 1 to n = 3 and approach to the bulk value of 2.25 eV at n = 4 and 5, consistent with the convergence of the structural parameters.
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