The photoelectron circular dichroism (PECD) of the O 1s-photoelectrons of trifluoromethyloxirane (TFMOx) is studied experimentally and theoretically for different photoelectron kinetic energies. The experiments were performed employing circularly polarized synchrotron...

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We directly observe radiative charge transfer (RCT) in Ne clusters by dispersed vacuum-ultraviolet photon detection. The doubly ionized Ne 2+ -Ne n 1 -initial states of RCT are populated after resonant 1s-3p photoexcitation or 1s photoionization of Ne n clusters with n 2800 á ñ » . These states relax further producing Ne + -Ne + -Ne n 2 -final states, and the RCT photon is emitted. Ab initio calculations assign the observed RCT signal to the Ne 2p D Ne ninitial state, while transitions from other possible initial states are proposed to be quenched by competing relaxation processes. The present results are in agreement with the commonly discussed scenario, where the doubly ionized atom in a noble gas cluster forms a dimer which dissipates its vibrational energy on a picosecond timescale. Our study complements the picture of the RCT process in weakly bound clusters, providing information which is inaccessible by charged particle detection techniques.

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It is commonly accepted that the magnitude of a photoelectron circular dichroism (PECD) is governed by the ability of an outgoing photoelectron wave packet to probe the chiral asymmetry of a molecule. To be able to accumulate this characteristic asymmetry while escaping the chiral ion, photoelectrons need to have relatively small kinetic energies of up to a few tens of electron volts. Here, we demonstrate a substantial PECD for very fast photoelectrons above 500 eV kinetic energy released from methyloxirane by a participator resonant Auger decay of its lowermost O 1s-excitation. This effect emerges as a result of the Fano interference between the direct and resonant photoionization pathways, notwithstanding that their individual effects are negligibly small. The resulting dichroic parameter has an anomalous dispersion, i.e. it changes its sign across the resonance, which can be considered as an analogue of the Cotton effect in the X-ray regime. 32.80.Hd, 33.55.+b, 81.05.Xj Photoelectron circular dichroism (PECD) is a fundamental chiroptical effect causing a forward-backward asymmetry in the laboratory-frame angular distribution of photoelectrons emitted from chiral molecules in the gas phase. PECD was first predicted theoretically for one-photon ionization [1-3] and then verified in pioneering experiments with circularly polarized synchrotron radiation [4,5]. The effect persists also in the multiphoton ionization regime using intense laser pulses [6,7]. Because PECD is a pure electric-dipole effect, it is much stronger than the traditional CD in the photoabsorption spectra of chiral molecules [8]. This fact, together with its enantioselectivity, has established PECD as a powerful tool for chiral recognition in the gas phase [8][9][10][11].Ritchie [1-3] has proven analytically that PECD arises due to an incomplete compensation of the contributions from emitted partial electron waves with different projections ±m of the carried angular momentum ℓ. Such an inequivalence occurs only for chiral molecules and has a twofold origin: It is induced by the chiral asymmetries of both, the initial bound and the final continuum electronic states entering the dipole-transition amplitudes. For slow photoelectrons with kinetic energies of a few electron volts, initial and final state contributions to PECD can be comparable [12]. As the electron kinetic energy grows, the photoelectron wave packet escapes the molecular ion quickly and does not have enough time to adopt its chiral asymmetry. In other words, both, the chiral initial state and the chiral potential of the ion can be considered almost symmetric for very fast photoelectrons. As a consequence, at high kinetic energies, typically at a few tens of electron volts [12,13] and in extreme cases at about 70 eV [14], PECD vanishes.In the present work, we demonstrate a very general mechanism of PECD recovery for electrons with kinetic energies of as high as a few hundreds of electron volts. This scenario involves an intermediate electronic resonance, which enables an excited m...