Photoelectron and photoion study of the valence photoionization of C60

Recent photoion yield measurements, done in the valence photoionization region of C60, reveal a high fraction of doubly and even triply charged ions [see A. Reinköster, S. Korica, G. Prümper, J. Viefhaus, K. Godehusen, O. Schwarzkopf, M. Mast, U. Becker, J. Phys. B: At. Mol. Opt. Phys. 37 (2004) 2135]. The Click to view the MathML source intensity increases continously up to hν≈60 eV and stays constants at higher photon energies. Moreover, the fragmentation into Click to view the MathML source and Click to view the MathML source is pronounced in the energy region hν≈50–70 eV. The question arises, if after electrons are removed from certain electronic levels, the multiple-ionization or even the fragmentation is somehow triggered. Or in other words, if the multiple-ionization or the fragmentation characteristics can be already seen in the simple (non-coincident) electron data. We can answer the question with the help of such non-coincident valence electron measurements, recorded in the interesting photon energy region hν≈40–70 eV

Energy and angular distributions of electrons emitted by direct double Auger decay

We have observed the direct L2,3MMM double Auger transition after photoionization of the 2p shell of argon by angle-resolved electron-electron coincidence spectroscopy. The process is responsible for about 20% of the observed Auger electron intensity. In contrast to the normal Auger lines, the spectra in double Auger decay show a continuous intensity distribution. The energy and angular distributions of the emitted electrons allow one to obtain information on the electron correlations giving rise to the double Auger process as well as the symmetry of the associated two-electron continuum state

Upper limits for stereoselective photodissociation of free amino acids in the vacuum ultraviolet region and at the C 1s edge

We measured the total and partial ion yields of the two chiral amino acids alanine and serine in the gas phase both in the vacuum ultraviolet region and at the C(1s) edge using circularly polarized light. We did not detect any circular dichroism asymmetry larger than 1×10–3. A similar measurement of fixed-in-space amino acids yielded an upper limit of 1×10–2 for the stereoselective effect of circularly polarized light. The results obtained are relevant for quantitative models of stereoselective photodecomposition of amino acids that try to explain the homochirality of life

Probing the transition from non-localization to localization by K-shell photoemission from isotope-substituted N2N_{2}

In homonuclear diatomic molecules such as N_2, 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

Localization and loss of coherence in molecular 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 N_2 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, Δp_xΔx and ΔEΔt, the second of which causes ongoing tunnelling between the two centres, even after the collapse of the electron wavefunction in real space