Search results for "Photoionization"
showing 10 items of 76 documents
A laser desorption/resonance enhanced photoionisation TOF-system for the spatially resolved trace analysis of elements
2004
Abstract A novel method for direct and spatially resolved elemental trace analysis with high sensitivity and elemental selectivity is presented. The concept is based on the combination of a commercial MALDI-TOF mass spectrometer with a pulsed laser system for resonant postionisation of neutrals. While the MALDI method is usually applied for investigations of large organic compounds and biomolecules, the technique discussed here concerns the low mass range around 1 ⩽ A ⩽ 300. The analytical performances of the setup with respect to mass analysis, spatial resolution and overall detection efficiency are discussed.
Binding site of different tannins on a human salivary proline-rich protein evidenced by dissociative photoionization tandem mass spectrometry
2015
Abstract The sensation of astringency is thought to originate from the interaction occurring between tannins and the salivary proline-rich proteins (PRPs). Astringency perception can be modified by the structure of tannins. Herein, we study the interactions occurring between the human salivary PRP, IB5, and three model tannins with different structure, epigallocatechin gallate and the procyanidin dimers B2 and B2 3′ O -gallate, using the coupling of mass spectrometry and VUV-synchrotron radiation. The results obtained indicate that the structure of tannins, in particular the degree of polymerization and the galloylation, does not modify the binding site on IB5 involved in the interaction.
From Above Threshold Ionization to Statistical Electron Emission: The Laser Pulse-Duration Dependence ofC60Photoelectron Spectra
2000
The photoelectron spectra of C60 ionized using a 790 nm laser with pulse durations varying from 25 fs to 5 ps have been determined. For 25 fs pulses, in the absence of fragmentation, the ionization mechanism is direct multiphoton ionization with clear observation of above threshold ionization. As the pulse duration is increased, this becomes dominated by a statistical ionization due to equilibration among the electronic degrees of freedom. For pulse durations on the order of a ps coupling to the vibrational degrees of freedom occurs and the well-known phenomenon of delayed (ms) ionization is observed.
A high-temperature laser ion source for trace analysis and other applications
1990
We report here on the development of a high-temperature laser ion source useful for trace analysis and other applications. It consists of a high temperature ionization chamber, three tunable dye lasers pumped by copper vapor lasers for stepwise resonant ionization and a Mattauch-Herzog mass spectrometer for the analysis of photo-ions. The principle of the laser ion source and its theoretical efficiency are discussed, where the efficiency of a laser ion source is the ratio of photo-ions extracted out to the number of atoms introduced into the cavity. Experimentally, an efficiency of 2×10−3 has been achieved for technetium. The scheme of gated detection is described which is used for suppress…
Electronic Structure Changes across the Metamagnetic Transition in FeRh via Hard X-Ray Photoemission
2012
International audience; Stoichiometric FeRh undergoes a temperature-induced antiferromagnetic (AFM) to ferromagnetic (FM) transition at similar to 350 K. In this Letter, changes in the electronic structure accompanying this transition are investigated in epitaxial FeRh thin films via bulk-sensitive valence-band and core-level hard x-ray photoelectron spectroscopy with a photon energy of 5.95 keV. Clear differences between the AFM and FM states are observed across the entire valence-band spectrum and these are well reproduced using density-functional theory. Changes in the 2p core levels of Fe are also observed and interpreted using Anderson impurity model calculations. These results indicat…
Ionization potential of aluminum clusters
1998
Structure, electronic structure, and ionization potential of aluminum clusters of 2–23 atoms are studied with a total energy method based on the density-functional theory. The calculated adiabatic ionization potentials agree remarkably well with the data from threshold photoionization measurements. The analysis of results gives insight into hybridization effects in the smallest clusters as well as reveals certain clusters that exhibit a clear jellium-type shell structure. An explanation of the experimental results in the size region of 12–23 atoms is given in terms of coexisting, competing icosahedral, decahedral, and fcc-based clusters. @S0163-1829~98!00228-8#
Isotope shifts and hyperfine structure in the transitions of gadolinium
2000
High-resolution resonance ionization mass spectrometry has been used to measure isotope shifts and hyperfine structure in all (J = 2-6) and the transitions of gadolinium (Gd I). Gadolinium atoms in an atomic beam were excited with a tunable single-frequency laser in the wavelength range of 422-429 nm. Resonant excitation was followed by photoionization with the 363.8 nm line of an argon ion laser and resulting ions were mass separated and detected with a quadrupole mass spectrometer. Isotope shifts for all stable gadolinium isotopes in these transitions have been measured for the first time. Additionally, the hyperfine structure constants of the upper states have been derived for the isotop…
Multi-color resonance ionization of laser ablated gadolinium at high laser power
2005
Abstract Spectroscopic and analytical properties of a trace analytical method using multi-step resonance ionization at high laser intensities (>kW/cm 2 ) have been investigated with gadolinium as a test element. Strongly saturated transitions are observed, which have been used for a temperature determination of the atoms in the laser ablated plume. Regimes of multi-step resonance ionization and multiphoton ionization could be distinguished. Analytical performances due to resonance enhancement and resulting discrimination against non-resonant background, precision in isotope ratio determination and overall detection efficiency are discussed.
First observation of a resonance ionization signal on242mAm fission isomers
1992
The feasibility of a hyperfine spectroscopy on242mAm fission isomers has been demonstrated at the low target production rate of 10/s. The experimental method employed is based on resonance ionization spectroscopy in a buffer gas cell with detection of the ionization process by means of the fission decay of the isomers. The resonance ionization has been performed in two steps, utilizing an excimer dye laser combination with a repetition rate of 300 Hz. The first resonant step proceeds through theJ=7/2 term at 21440.35 cm−1, which has been excited with the tuncable dye laser beam of a wavelength of 466.28 nm, the second non-resonant step is achieved with the 351 nm radiation of the excimer la…
Nuclear shape transition in neutron-deficient gold isotopes
1987
4 pages, 1 table, 4 figures.