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...

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The time scale for electronic reorganization upon sudden ionization of the water and water-methanol hydrogen bonded dimers and of the weakly bound NO dimer

It is demonstrated that excited van der Waals systems can relax by electron emission via a novel interatomic mechanism. The process is analyzed by means of extensive ab initio calculations of potential energy surfaces and electronic decay rates. The electronic emission, taking place on the same time scale as the motion of the atomic nuclei, is accompanied by interesting dynamical effects amenable to experimental observations. These effects arise as a consequence of the weak chemical bond in van der Waals clusters and the Coulomb repulsion pattern originating from electron emission.