In sharp contrast to molecules, electronic states of clusters with an excited intermediate-shell electron can efficiently decay via an intermolecular Coulombic mechanism. Explicit examples are presented using large scale ab initio propagator calculations. The mechanism is illustrated and its generality is stressed. [S0031-9007(97) PACS numbers: 36.40.Cg, 31.50. + w, 34.50.Gb Quantum states of electronic systems typically decay by photon and/or electron emission. Energetically low lying states decay radiatively while highly excited levels involving the excitation of inner-shell electrons decay more efficiently by emitting an electron (Auger decay). It is only for very deep inner-shell electrons of heavy elements that x-ray emission constitutes the prominent decay channel [1]. States which can decay only radiatively, i.e., states with excited outer-shell electrons, exhibit an exceedingly long lifetime (ഠ nanoseconds) compared to Auger-decaying states. For instance, a vacancy in the 1s shell of a fluorine atom has a lifetime of about 3.3 fs (0.20 eV linewidth) [2]. This lifetime depends only weakly on whether the fluorine atom is free or integrated in a molecular system. The total decay rate is essentially determined by the neighboring atomic electrons. Deeper electron vacancies typically decay faster. An excited or ionized state of the sulfur atom with a vacancy in the 1s shell, for example, lives for about 1.6 fs [3], and if the vacancy is in the 2p shell the lifetime extends to 66 fs [4].As mentioned above, the environment of the atom influences only moderately the lifetime of the deep vacancy (e.g., of a F1s vacancy). If at all, we can only expect interesting environmental effects on the total Auger decay rate to take place for vacancies in intermediate shells.However, a closer look at the energetics of the decay in typical molecules brings a problem to light. The ionization potential (IP) of a F2s electron in, say, the HF molecule, is about 40 eV [5], but the release of these 40 eV is insufficient to ionize a second electron: the lowest double ionization potential (DIP) of HF is about 45 eV [6]. Similarly, the IP of an O2s electron in H 2 O is approximately 35 eV [7], again too small an energy to allow a second electron to leave the system. The lowest DIP of water is about 38 eV [8]. The situation changes substantially as we move to clusters. While the IP of intermediate shells differs only slightly from that of the monomer unit, some DIPs are lowered considerably in the cluster and the autoionization channel opens. More importantly, we shall also show in this Letter that the accessible decay becomes dramatically efficient in clusters.Atomic and molecular clusters have been subject to continuous interest over many years [9][10][11]. Most of the interest has been devoted to the possible geometrical structures and properties of the clusters in their electronic ground state. Much less attention has been paid to excited electronic states and no attention to highly excited states involving intermediate shell ele...
The nature of the chemical bond between gold and the noble gases in the simplest prototype of Au(I) complexes (NgAuF and NgAu+, where Ng = Ar, Kr, Xe), has been theoretically investigated by state of art all-electron fully relativistic DC-CCSD(T) and DFT calculations with extended basis sets. The main properties of the molecules, including dipole moments and polarizabilities, have been computed and a detailed study of the electron density changes upon formation of the Ng-Au bond has been made. The Ar-Au dissociation energy is found to be nearly the same in both Argon compounds. It almost doubles along the NgAuF series and nearly triples in the corresponding NgAu+ series. The formation of the Ng-Au(I) bonds is accompanied by a large and very complex charge redistribution pattern which not only affects the outer valence region but reaches deep into the core-electron region. The charge transfer from the noble gas to Au taking place in the NgAu+ systems is largely reduced in the fluorides but the Ng-Au chemical bond in the latter systems is found to be tighter near the equilibrium distance. The density difference analysis shows, for all three noble gases, a qualitatively identical nature of the Ng-Au bond, characterized by the pronounced charge accumulation in the middle of the Ng-Au internuclear region which is typical of a covalent bond. This bonding density accumulation is more pronounced in the fluorides, where the Au-F bond is found to become more ionic, while the overall density deformation is more evident and less localized in the NgAu+ systems. Accurate density difference maps and charge-transfer curves help explain very subtle features of the chemistry of Au(I), including its peculiar preference for tight linear bicordination.
We definitively show that the CO stretching response to metal coordination is driven exclusively by π polarization, which quantitatively correlates with π back-donation and changes in CO bond length and frequency.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.