Because of inversion symmetry and particle exchange, all constituents of homonuclear diatomic molecules are in a quantum mechanically non-local coherent state; this includes the nuclei and deep-lying ...core electrons. Hence, the molecular photoemission can be regarded as a natural double-slit experiment: coherent electron emission originates from two identical sites, and should give rise to characteristic interference patterns. However, the quantum coherence is obscured if the two possible symmetry states of the electronic wavefunction ('gerade' and 'ungerade') are degenerate; the sum of the two exactly resembles the distinguishable, incoherent emission from two localized core sites. Here we observe the coherence of core electrons in N(2) through a direct measurement of the interference exhibited in their emission. We also explore the gradual transition to a symmetry-broken system of localized electrons by comparing different isotope-substituted species--a phenomenon analogous to the acquisition of partial 'which-way' information in macroscopic double-slit experiments.
In molecular double-slit experiments, the interference between emitted core electrons of diatomic molecules gives rise to oscillations in the observed electron intensity. Here, we explore this ...behaviour for photoelectrons emitted from CO and N2 by soft X-ray ionization in the molecular frame, and we argue that in addition to the undisturbed emission process, intramolecular scattering can lead to electron interference between the scattered and unscattered wave in two ways: two-centre interference between two spatially coherent emitters and one-centre self-interference. The latter is the signature of a loss of spatial coherence. The spatial scale over which the transition from two-centre to one-centre coherence occurs is the de Broglie wavelength of the scattered photoelectron in units of the bond length. These results highlight the fact that the molecular double slit is based on two independent uncertainty principles, DeltapxDeltax and DeltaEDeltat, the second of which causes ongoing tunnelling between the two centres, even after the collapse of the electron wavefunction in real space. PUBLICATION ABSTRACT
Appearance of Plasmons in Fullerenes Korica, Sanja; Reinköster, Axel; Braune, Markus ...
Journal of physics. Conference series,
01/2012, Letnik:
388, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The valence electrons of fullerenes may be regarded as spherical distributions with a finite width of a jellium-like potential giving rise to collective motions of this orange peel electron cloud. ...They cause strong enhancement of the photoionization cross section, a resonant behavior phenomenon know as plasmon excitations. The number and characteristic features of these excitations will be discussed.
The (multiple) photoionization and subsequent fragmentation of the C60 molecule was studied with the synchrotron radiation after removing electrons from the inner K-shell. Our intention was ...especially focused on the dynamics of the subsequent fragmentation. In addition to ’normal’ (non-coincident) electron and ion time-of-flight spectroscopy, we investigated this topic with the help of an electron–electron-coincidence measurement. Our experiment shows that in these processes Cq+ 60 ions with charge states up to 3+ and several smaller Cq+ 60-2m fragments are formed. In addition, the broad peak besides the C(1s) line, usually referred to as the 'plasmon' peak, has been observed. / (Многогранная) фотоионизация и сопроводительная фрагментация молекулы C60 исследовалась с помощью синхротронного излучения после выброса электрона из внутренней К-оболочки. Наше исследование было сосредоточено на динамике сопроводительной фрагментации. Кроме «нормальной» (несовпадающей) электронной и ионной спектроскопии, применялись и другие методы измерений, так например, было проведено измерение электронного совпадения. Наш эксперимент показал, что в течение этих процессов формируются Cq+ 60 ионы с зарядом до трех + и несколько небольших Cq+ 60-2m фрагментов. Кроме того, был выявлен широкий пик рядом с основной линией C (1s), так называемым «плазмоном». / Fotojonizacija (višestruka) i prateća fragmentacija molekula C60 proučavana je uz pomoć sinhrotronskog zračenja nakon izbacivanja elektrona iz unutrašnje K-ljuske. Naše istraživanje bilo je posebno fokusirano na dinamiku prateće fragmentacije. Pored 'normalne' (nekoincidentne) elektronske i jonske TOF spektroskopije, ovu temu izučavali smo i uz pomoć elektron-elektron koincidentnog merenja. Naš eksperiment pokazuje da se u ovim procesima formiraju Cq+60 joni sa naelektrisanjem do 3+ i nekoliko manjih Cq+60-2m fragmenata. Pored toga, pored glavne C(1s) linije uočen je široki pik, tzv. plazmon.
One of the important characteristics of the C60 molecule is the collective response of its valence electron cloud to the electromagnetic radiation. This collective behavior gives rise to the ...occurrence of the giant dipole resonance (so called surface plasmon) in the absorption spectrum centered around 20 eV, which has also been analyzed theoretically by various authors. Concerning photoelectron emission, plasmonic excitation is characterized by a particular intensity behavior near the threshold. We present here a new series of the K-shell photoelectron spectra with particular emphasis on the qualitative analysis of all ionization with excitation and double ionization processes. Our measurements of the C60 plasmon excitation follow the so-called Thomas-Derrah law and are in good agreement with the corresponding behavior of satellite excitations in atoms such as neon. / Одной из самых значительных свойств молекулы С60 является коллективная реакция ее валентных электронов на электромагнитные излучения. Вследствие коллективной реакции в спектре поглащения возникает огромный дипольный резонанс (так называемый поверхностный плазмон), приблизительно на 20 eV, который был неоднократно представлен различными авторами в их теоретических исследованиях. В случае фотоэлектронной эмиссии, наблюдаются характерное поведение плазмонов при возбуждении на пороге ионизации. В работе представлена новая серия фотоэлектронных спектров Коболочки, а также подробный квалитативный анализ всех ионизаций с возбуждениями в процессе двойной ионизации. На основании проведенного анализа и измерений плазмонного возбуждения С60 при применении так называемого закона ТомасДерраха можно утверждать, что они полностью совпадают с соответствующим поведением сателлитного возбуждения атомов в неонах. / Jedna od značajnih karakteristika C60 molekula je kolektivni odgovor njegovih valentnih elektrona na elektromagnetno zračenje. Ovo kolektivno ponašanje dovodi do pojave ogromne dipolne rezonance (tzv. površinski plazmon) u apsorpcionom spektru na oko 20 eV, koji su različiti autori i teorijski analizirali. Kada je u pitanju fotoelektronska emisija, plazmonsku ekscitaciju karakteriše posebno ponašanje na pragu jonizacije. Prikazana je nova serija fotoelektronskih spektara K-ljuske sa težištem na kvalitativnoj analizi svih jonizacija sa ekscitacijama i procesima dvostruke jonizacije. Merenja plazmonske ekscitacije S60 prate tzv. Tomas-Dirahov zakon i u velikoj su saglasnosti sa odgovarajućim ponašanjem satelitskih ekscitacija u atomima kao što je neon.
Because of inversion symmetry and particle exchange, all constituents of homonuclear diatomic molecules are in a quantum mechanically non-local coherent state; this includes the nuclei and deep-lying ...core electrons. Hence, the molecular photoemission can be regarded as a natural double-slit experiment: coherent electron emission originates from two identical sites, and should give rise to characteristic interference patterns. However, the quantum coherence is obscured if the two possible symmetry states of the electronic wavefunction ('gerade' and 'ungerade') are degenerate; the sum of the two exactly resembles the distinguishable, incoherent emission from two localized core sites. Here we observe the coherence of core electrons in N2 through a direct measurement of the interference exhibited in their emission. We also explore the gradual transition to a symmetry-broken system of localized electrons by comparing different isotope-substituted species-a phenomenon analogous to the acquisition of partial 'which-way' information in macroscopic double-slit experiments.
In homonuclear diatomic molecules such as N2, the inversion symmetry of the system causes non-local, coherent behavior of the otherwise localized core holes. The non-locality of the electron emission ...and the remaining core hole changes in a continuous way into partially localized behaviour if a gradual breakdown of the inversion symmetry is induced by isotope substitution. This is reflected by a loss of interference and a parity mixing of the outgoing photoelectron waves. Our results represent the first experimentally observed isotope effect on the electronic structure of a diatomic molecule.
Multi-photon ionization for all rare gases by radiation from the Free Electron Laser FLASH in Hamburg is reported. The ionization events are analyzed by angle resolved electron Time-of-Flight ...spectroscopy. Photoelectrons belonging to different coupling schemes of the final ionic state are energetically resolved and their angular distributions could be determined separately for all three final ionic states for the first time. The behavior of the multi-photon specific term β4 shows different values for different final ionic states pointing to coupling scheme dependent anisotropic final state interactions.
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