303 research outputs found
EUV ionization of pure He nanodroplets: Mass-correlated photoelectron imaging, Penning ionization and electron energy-loss spectra
The ionization dynamics of pure He nanodroplets irradiated by EUV radiation
is studied using Velocity-Map Imaging PhotoElectron-PhotoIon COincidence
(VMI-PEPICO) spectroscopy. We present photoelectron energy spectra and angular
distributions measured in coincidence with the most abundant ions He+, He2+,
and He3+. Surprisingly, below the autoionization threshold of He droplets we
find indications for multiple excitation and subsequent ionization of the
droplets by a Penning-like process. At high photon energies we evidence
inelastic collisions of photoelectrons with the surrounding He atoms in the
droplets
Synchrotron radiation photoionization mass spectrometry of laser ablated species
The present paper describes an experimental apparatus suitable to create and study free clusters by combining laser ablation and synchrotron radiation. First tests on sulfur samples, S, showed the production, through laser ablation, of neutral Sn clusters (n = 1–8). These clusters were ionized using synchrotron radiation at photon energies from 160 eV to 175 eV, across the S 2p core edge. The feasibility of such combined ablation–synchrotron radiation experiments is demonstrated, opening new possibilities on the investigation of free clusters and radical
Penning ionization of doped helium nanodroplets following EUV excitation
Helium nanodroplets are widely used as a cold, weakly interacting matrix for
spectroscopy of embedded species. In this work we excite or ionize doped He
droplets using synchrotron radiation and study the effect onto the dopant atoms
depending on their location inside the droplets (rare gases) or outside at the
droplet surface (alkali metals). Using photoelectron-photoion coincidence
imaging spectroscopy at variable photon energies (20-25 eV), we compare the
rates of charge-transfer to Penning ionization of the dopants in the two cases.
The surprising finding is that alkali metals, in contrast to the rare gases,
are efficiently Penning ionized upon excitation of the (n=2)-bands of the host
droplets. This indicates rapid migration of the excitation to the droplet
surface, followed by relaxation, and eventually energy transfer to the alkali
dopants
VUV and X-ray coherent light with tunable polarization from single-pass free-electron lasers
Tunable polarization over a wide spectral range is a required feature of
light sources employed to investigate the properties of local symmetry in both
condensed and low-density matter. Among new-generation sources, free-electron
lasers possess a unique combination of very attractive features, as they allow
to generate powerful and coherent ultra-short optical pulses in the VUV and
X-ray spectral range. However, the question remains open about the possibility
to freely vary the light polarization of a free-electron laser, when the latter
is operated in the so-called nonlinear harmonic-generation regime. In such
configuration, one collects the harmonics of the free-electron laser
fundamental emission, gaining access to the shortest possible wavelengths the
device can generate. In this letter we provide the first experimental
characterization of the polarization of the harmonic light produced by a
free-electron laser and we demonstrate a method to obtain tunable polarization
in the VUV and X-ray spectral range. Experimental results are successfully
compared to those obtained using a theoretical model based on the paraxial
solution of Maxwell's equations. Our findings can be expected to have a deep
impact on the design and realization of experiments requiring full control of
light polarization to explore the symmetry properties of matter samples
On the production of N-2(+) ions at the N 1s edge of the nitrogen molecule
The N+2 ion yield of the N2 molecule has been measured at the N 1s → Rydberg excitations. It displays Fano-type line shapes due to interference between direct outer-valence photoionization and participator decay of the core-excited Rydberg states. The N+2 ion yield is compared with the total intensity of the outer-valence photoelectron lines obtained recently with electron spectroscopy (Kivimäki et al 2012 Phys. Rev. A 86 012516). The increasing difference between the two curves at the higher core-to-Rydberg excitations is most likely due to soft x-ray emission processes that are followed by autoionization. The results also suggest that resonant Auger decay from the core–valence doubly excited states contributes to the N+2 ion yield at the photon energies that are located on both sides of the N 1s ionization limit
On the possibility to utilize a PCO Edge 4.2 bi scientific CMOS imager for extended ultra violet and soft X-ray photon detection
A state of the art commercial detector, a PCO Edge 4.2 bi based on a back illuminated sCMOS sensor developed for applications in the visible light/ultra violet regime has been adapted for ultra-high vacuum operations and has been characterized using soft X-ray in the energy range from 30 eV to 1000 eV. The imager features 2048 x 2048 pixel with a pixel size of 6.5 mu m x 6.5 mu m and allows full frame acquisitions at 48 Hz with a dynamic range of 88 dB at a noise level of 1.9 e(-). Spatial resolution and quantum efficiency have been elucidated in the aforementioned energy range at a soft X-ray beam line at Elettra Sincrotrone Trieste. The handiness of the camera as well as its Python library package allows easy and fast integration into the beam line environments of synchrotron sources and free electron lasers
An experimental and theoretical study of the resonant Auger spectrum of the ethene molecule
Resonant Auger spectra of the ethene molecule excited at energies across the
C1s → π* energy band are reported. Our measurements address the unexpected
variation of the intensity of the A state with respect to the other singly ionized
valence states. An approach, based on group theory and calculations using
Coulomb 4-center integrals, is proposed to explain the behaviour of the intensity
of the ground state and excited states of the ion upon resonant excitation. The
new method provides a calculationally inexpensive route to predict relative
intensities of different resonant Auger bands in polyatomic molecules, without
the need for an exhaustive knowledge of the potential energy surfaces of the
electronic states involved
An experimental and theoretical investigation of XPS and NEXAFS of nicotine, nicotinamide, and nicotinc acid
The electronic structures of nicotine, nicotinic acid and nicotinamide have been studied by valence
photoemission spectroscopy (PES), core X-ray photoelectron spectroscopy (XPS), and near-edge X-ray absorption fine structure (NEXAFS) and interpreted with the aid of quantum chemical calculations. Nicotinamide and
nicotinic acid are closely related and show correspondingly similar spectral features, while nicotine is both structurally and spectroscopically diverse
- …