Ruma De

Plasmon?plasmon coupling in nested fullerenes: photoexcitation of interlayer plasmonic cross modes

Considering the photoionization of a two-layer fullerene?onion system, C60@C240, strong plasmonic couplings between the nested fullerenes are demonstrated. The resulting hybridization produces four cross-over plasmons generated from the bonding and antibonding mixing of excited charge clouds of individual fullerenes. This suggests the possibility of designing buckyonions exhibiting plasmon resonances with specified properties and may motivate future research to modify the resonances with encaged atoms, molecules or clusters.

Coherence of Auger and inter-Coulombic decay processes in the photoionization of Ar@C60 versus Kr@C60

Abstract For the asymmetric spherical dimer of an endohedrally confined atom and a host fullerene, an innershell vacancy of either system can decay through the continuum of an outer electron hybridized between the systems. Such decays, viewed as coherent superpositions of the single-center Auger and two-center inter-Coulombic (ICD) amplitudes, are found to govern leading decay mechanisms in noble-gas endofullerenes, and are likely omnipresent in this class of nanomolecules. A comparison between resulting autoionizing resonances calculated in the photoionization of Ar@C60 and Kr@C60 exhibits details of the underlying processes. Graphical abstract

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

Considering the photoionization of Ar@C60, we predict resonant femtosecond decays of both Ar and C60 vacanciesthroughthecontinuaofatom-fullerenehybridfinalstates.ForAr3s → np excitations,theseresonances are far stronger than the Ar-to-C60 resonant intersite-Coulombic decays (ICD), while for C60 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, offering a unique probe, more powerful than regular ICDs, for multicenter decay processes.

First prediction of the direct effect of a confined atom on photoionization of the confining fullerene

We predict that the confined atom can qualitatively modify the energetic photoionization of some cage levels, even though these levels are of very dominant fullerene character. The effect imposes strong new oscillations in the cross sections which are forbidden to the ionization of empty fullerenes. Results are presented for the Ar@C60 endofullerene compound.

Photoionization of open-shell halogen atoms endohedrally confined in C60

Endofullerene molecules, formed by encapsulating atoms in fullerenes, are extremely stable form of nanoscopic matters that can exist even at room temperature. Since these entrapments have lower-cost sustenance than the laser cooling or magneto-optical trapping processes, endofullerenes are unique natural laboratories to study not only the greatly modified properties of the confined atomic system but also the confining fullerene. Notable effects include the electronic hybridization between guest-host systems [1] and strong spectral processes, such as, the plasmon excitations and quantum diffraction intrinsic to response of these molecules [2]. A number of studies have been conducted for endofullerenes involving closed shell atoms, while there have been little research on systems that confine open shell atoms. In this study, using a jellium-based local density approximation (LDA) method [1], augmented by the LB94 exchange-correlation functional [3], we model the ground state of endofullerenes encaging three halogen atoms, Cl, Br and I, which are one np electron shy of the shell closure. Strong atomC60 hybridization in the np levels is found which, however, shows a systematic weakening trend from Cl to I. The dipole photoionization cross sections of these hybrid levels are calculated in a timedependent LDA which includes linear response electron correlations [3]. Results for Cl@C60 are presented in Figure 1. The narrow spikes in the cross sections are routine resonances from the Auger-type decay of inner-shell excitations. Comparing with the free atom 3p result, the cross sections for the bonding and antibonding hybrid levels broadly display two energy regions: (i) plasmon-enhanced low-energy domain and (ii) broad oscillations from the coherence of cavity and confinement effects at higher energies. However, even within this generic shape, results reveal significant differences in the details of the results between the hybrid levels. While the bonding level features stronger effects of the plasmons and a strong atomic character at higher energies, the antibonding ionization dramatically diminishes at higher energies suggesting dominant C60 emission.

First prediction of inter-Coulombic decay of C60 inner vacancies through the continuum of confined atoms

Considering the photoionization of Ar@ and Kr@ endofullerenes, the decay of innershell excitations through the outershell continuum of the confined atom via the inter-Coulombic decay (ICD) pathway is detailed. Excitations to atom- hybrid states, when these states exist, can induce coherence between ICD and electron-transfer mediated decay (ETMD). This should be the dominant above-threshold decay process for a variety of confined systems, and the strength of these resonances is such that they should be amenable for study by photoelectron spectroscopy.

Photoionization of bonding and antibonding-type atom-fullerene hybrid states in Cd@C60 vs Zn@C60

Powerful hybridization of the Cd 4d state with the d-angular momentum state of C60 π symmetry is found in the local density approximation (LDA) structure of Cd@C60 ground state. The photoionization of the resulting symmetric and antisymmetric levels are computed using the time dependent LDA method to include electron correlations. Cross sections exhibit effects of the C60 plasmonic motion coherently coupled to the diffraction-type cavity oscillations induced by local emissions from C60. The Cd@C60 results exhibit a substantial difference from our previous results for Zn@C60.

Auger-intercoulombic hybridized decay resonances in Kr@C60

We predict resonant hybridization of Auger and intercoulombic decay (ICD) processes in the photoionization of Kr@C60 using the time-dependent local density approximation (TDLDA) for the calculation.