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

Abstract

Considering the photoionization of Ar@C 60 , we predict resonant femtosecond decays of both Ar and C 60 vacancies through the continua of atom-fullerene hybrid final states. The resulting resonances emerge from the interference between simultaneous autoionizing and intercoulombic decay (ICD) processes. For Ar 3s → np excitations, these resonances are far stronger than the Ar-to-C 60 resonant ICDs, while for C 60 excitations they are strikingly larger than the corresponding Auger features. The results indicate the power of hybridization to enhance decay rates, and modify lifetimes and line profiles. [4] research has gone into studying ICD processes in weakly bound atomic systems. These involve the observation of ICD in rare gas dimers [5], rare gas clusters [6], surfaces [7], and small water droplets [8,9]. 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] Of particular interest is the resonant ICD (RICD) where the precursor excitation to form an inner-shell vacancy is accomplished by promoting an inner electron to an excited state by an external stimulant, generally electromagnetic radiation [17,18] or, more recently, chargeparticle impact [21]. A theoretical study of RICD followed by Ne 2s → np excitations in MgNe clusters suggested the leading contribution of RICD among other interatomic decay modes [22]. Photoelectron spectroscopy with Ne clusters for 2s → np excitations measured the signature of RICD processes [17]. Similar excitations in the double photoionization of Ne dimers were utilized to observe RICD by tracking the formation of energetic Ne + fragments [18]. Most recently, strong enhancement of the HeNe + yield, as He resonantly couples with the radiation, is detected [19], confirming an earlier prediction [20].Atoms confined in fullerene shells forming endofullerene compounds are particularly attractive natural laboratories to study RICD processes. There are two compelling reasons for this: (i) such materials are highly stable, have low-cost sustenance at the room temperature and are enjoying a rapid improvement in synthesis techniques [23]; and (ii) the effect of correlation of the central atom with the cage electrons have been predicted to spectacularly affect the atomic photoionization [24]. A first attempt to predict ICD in endofullerenes was made by calculating ICD rates for Ne@C 60 [25]. While some speculation on the role of Coulomb interaction mediated energy transfer from atom to fullerene to broaden Auger lines has been made [26,27], no studies, theoretical or experimental, of RICD resonances in the ionization cross section of endofullerenes have been performed. Furthermore, ICD of endofullerene molecules can uncover effects not yet known. This is because: (i) endofullerenes being spherical analogues of asymmetric dimers consisting of an atom and a cluster can also induce reverse RICD processes, the decay of...

The influence of retardation and dielectric environments on interatomic Coulombic decay

“…However, they cannot easily deal with the effects of retardation stemming from the finite speed of light. Furthermore, while a simple dielectric background or extended host molecule can be taken into account with molecular dynamics techniques 15 , 16 or via numerical quantum chemistry 17 – 19 , the full effects of dispersion, absorption, relativistic retardation and sharp boundaries remain computationally beyond reach. This means that such approaches are not able to account for the effects of a complex environment, such as that of a helium nanodroplet 20 – 23 or those found in biological settings 10 , 24 , 25 .…”

Electron elastic scattering offA@C60: The role of atomic polarization under confinement

“…Note, a meager amount of research on e+A@C 60 collision is in contrast to the study of photon-A@C 60 collision, different aspect of which has been intensely scrutinized in a great variety of theoretical works to date (see, e.g., Refs. [7][8][9][10][11][12][13][14] and references therein), including experimental studies [15,16] (and references therein). Such disbalance in favor of the number and quality of studies of A@C 60 photoionization versus research on electron-A@C 60 collision is not accidental.…”

Photoionization of endohedral atoms: Molecular and interchannel-coupling effects

“…The correlation is included through the use of time-dependent density functional theory (TDDFT) [21,22] which is an outgrowth of earlier work at just the DFT [19] level. As a first step we have chosen Ar@C 60 which has been the subject of a number of earlier studies [1,2,4,9,11,[23][24][25][26][27][28]. There are two questions which we are particularly interested in: how confinement resonances are affected by the inclusion and interaction of both the molecular structure and correlation; and how the inclusion of the C 1s channels of C 60 , and the interchannel coupling with these channels, affects the inner-shell atomic photoionization channels.…”