Dynamic two-center resonant photoionization in slow atomic collisions

Abstract

An additional channel for photoionization of an atom A by an electromagnetic field opens if it interacts with an atom B resonantly coupled to this field. In this channel, which is known to be very efficient when A and B constitute a bound system, A is ionized via resonant photoexcitation of B with subsequent energy transfer to A through two-center electron correlations. We show that it can strongly dominate the ionization of A also in collisions with B, even though the average distance between A and B exceeds the typical size of a bound system by orders of magnitude.The breakup of bound microscopic systems by photoabsorption is characterized by well defined energy and momentum transfers, which often enables one to extract precise information about the process and the system itself. Studies of photo-induced breakup reactions-such as atomic photoionization (PI) [1, 2], molecular photodissociation [3], and nuclear photo-disintegration [4]-therefore deepen our understanding of the structure and dynamics of matter on a microscopic scale. Notably, photoionization and photodissociation allow to probe the fundamental role played by electron correlations.Electron correlations are omnipresent in the quantum world, ranging from atoms and small molecules to organic macromolecules and solids. They drive autoionization of atoms and ions and mutual electron transitions in high-energy ion-atom collisions [5,6], can result in de-excitation reactions (e.g. Penning effect) in slow atomic collisions [7] and in ultracold quantum gases [8], govern energy transfer between chromophores [9] and lattice dynamics in polymers [10], and are even responsible for magnetism and superconductivity [11]. Electron correlations between atoms in bound systems with more than one atomic center lead to inter-atomic Coulombic decay (ICD) [12] observed in dimers and clusters [13-16] and water molecules [17]. Inter-atomic electron correlations can greatly enhance recombination processes [18,19] and lead to resonances in electron scattering on two-atomic systems [19].Particularly clean manifestations of electron correlations are revealed in some PI processes, e.g. in singlephoton double ionization [20], non-sequential double ionization in strong laser fields [21] and resonant twocenter PI [22]. In the latter, ionization of a large-size molecule occurs via resonant photoabsorption by one of its atoms with subsequent transfer of excitation energy via two-center electron correlations to another atom leading to its ionization. This two-center ionization channel can be remarkably effective and strongly dominate over the usual direct single-center PI. It was experimentally observed in helium-neon dimers using synchrotron radiation [23].In this communication we study a dynamic variant of resonant two-center PI occurring in slow atomic collisions (see figure 1). The average distance R between colliding atoms is (many) orders of magnitude larger than in a bound system and the probability for the two-center PI scales as R −6 [22]. Therefore, it might seem at first si...

Two-center resonant photoionization-excitation driven by combined intra- and interatomic electron correlations

“…Before moving on to the conclusion we briefly describe a variant of 2CPI that is related to 2CPIE. In the standard form of 2CPI, an atom B is resonantly photoexcited and, afterwards, deexcites back into its initial state (typically the ground state), transfering the energy release to a neighboring atom A which gets ionized [14][15][16][17]. However, as figure 3 shows, it is also conceivable that the deexcitation of atom B does not proceed fully down to the initial state, but instead to another excited state of intermediate energy.…”

“…Here, an atom B is first resonantly excited by photoabsorption and, afterwards, deexcites by transfering the excess energy radiationlessly to a neighboring atom A of different species, causing its ionization. This two-center resonant photoionization (2CPI) has been studied both theoretically [14][15][16][17][18] and experimentally [19,20] in recent years.…”

Interatomic and Intermolecular Coulombic Decay

“… 230 It can be seen as the inverse of two-center dielectronic recombination ( eq 4 ). More theoretical 33 , 52 , 154 , 231 , 233 , 402 and experimental 305 , 403 , 404 work has appeared.…”

Influence of nuclear motion on resonant two-center photoionization

“…It is worth mentioning that angular distributions of electrons emitted via 2CPI from He-Ne dimers have been calculated in [19], including their vibrational level structure (for a similar consideration of ICD in He 2 , see [21]). Besides, we note that 2CPI has recently been studied in slow atomic collisions where the internuclear distance is not fixed either but subject to the relative atomic motion which was assumed to follow a straight-line trajectory [22].…”