Ultrafast Interatomic Electronic Decay in Multiply Excited Clusters

Abstract

An ultrafast mechanism belonging to the family of interatomic Coulombic decay (ICD) phenomena is proposed. When two excited species are present, an ultrafast energy transfer can take place bringing one of them to its ground state and ionizing the other one. It is shown that if large homoatomic clusters are exposed to an ultrashort and intense laser pulse whose photon energy is in resonance with an excitation transition of the cluster constituents, the large majority of ions will be produced by this ICD mechanism rather than by two-photon ionization. A related collective-ICD process that is operative in heteroatomic systems is also discussed.PACS numbers: 31.70. Hq, 32.80.Rm, 32.80.Wr The rapid development during the last decades of very intense light sources with extreme short pulse duration opened a new era in the study of radiation-matter interaction. Studying the interaction of intense fields with matter brought to the discovery of a whole plethora of new physical phenomena, like high-harmonic generation, above-threshold ionization, or tunneling ionization, to name only a few. In the same time, the progress in generating extremely short pulses gave the scientific community a powerful tool to monitor and control the electron dynamics in atomic and molecular systems and to study processes that take place on a time scale in which the electronic motion is still disentangled from the slower nuclear dynamics (for recent reviews see, e.g., Refs. [1, 2]). A number of free-electron lasers are in operation today providing extremely bright, coherent, and ultrashort pulses in the VUV regime. Exposed to such highly intense pulses, atomic and molecular systems will absorb a large amount of photons triggering various dynamical effects. In this letter we will restrict ourselves to situations where the single-photon energy in the pulse is not high enough to directly ionize the system. It is well known that even in this case the system can be ionized by a multiphoton ionization mechanism. The multiphoton ionization (MPI) results from the ability of quantum systems to absorb several and even many photons, whose individual energies are insufficient to ionize the system. The combined energy of the absorbed photons, though, suffices to eventually eject one or many electrons from the system. During the last decade the MPI has been intensively studied also in composite systems, like clusters, employing the new powerful laser sources (for a review see, e.g. Ref.[3]). However, little attention was paid to other mechanisms that can lead to a multiple ionization in an atomic or molecular cluster irradiated by an intense laser pulse.In this letter we aim at discussing a hitherto unrecognized mechanism for producing ionized species in homoatomic or homomolecular clusters exposed to an intense laser pulse, which in many cases can be by far One of the constituents of the system de-excites transferring the energy to the neighbor which uses it to emit its excited electron.the dominating one. For simplicity we will consider an atomic cluste...

Extreme ultraviolet ionization of pure He nanodroplets: Mass-correlated photoelectron imaging, Penning ionization, and electron energy-loss spectra

“…In contrast to that, He droplets that are multiply excited by single intense ultrashort light pulses as available from free-electron lasers will autoionize by a different mechanism akin to interatomic Coulombic decay. 42,43 Thus, the Penning ionization process appears to be very efficient relative to the decay of He* or He * 2 excitations by spontaneous relaxation or by desorption off the droplet surface. This interpretation is supported by the results of earlier experiments studying the dynamics of excitations in bulk superfluid He and on molecular beam studies of He*-He* Penning collisions.…”

Resonant Auger–intersite-Coulombic hybridized decay in the photoionization of endohedral fullerenes

“…ICD followed by resonant Auger decay has been identified in Ar dimers using momentum resolved electron-ion-ion coincidence spectroscopy [10,11]. Ultrafast ICDs of a dicationic monomer in a cluster to produce a cluster tricataion [12] or multiply excited homoatomic cluster [13] were predicted. Also, time domain measurements of ICD in He [14] and Ne [15] dimers have recently been achieved.…”

Collective relaxation processes in atoms, molecules and clusters

“…Hence, collective decay can contribute substantially to the accumulation and redistribution of positive charges in a cluster exposed to ionizing radiation. Furthermore, collective ICD is expected to be even more significant if the cluster is initially multiply excited rather than ionized since under such conditions the multi-electronic process proceeds without the competition from cluster disintegration [20].…”

“…The ionization can proceed either via multiphoton absorption of a single atom or via absorption of single photons by multiple atoms followed by CAI. The basic mechanism underlying CAI is equivalent to two-electron ICD between two excited atoms as proposed by Kuleff et al [20], however, a number of alternative pathways involving three or more electrons may be operative [23]. Experimentally, CAI can be distinguished from multiphoton ionization by utilizing the first-order perturbation theory formula for the ionization rate…”

“…Related collective decay processes of multiply inner-valence ionized or excited clusters were recently proposed and observed experimentally [19,20,21]. Despite the significantly weaker interatomic correlation in van der Waals clusters as compared to molecules, it has been shown that higherorder decay pathways can play an important role, particularly if the two-electron radiationless decay channels are closed.…”