Resonance ionization spectroscopy with

Charge Neutralization and Resonance Ionization Spectroscopy with Amplification (RISA)... 

Hurst, G.S. Payne, M. G. Kramer, S.D. and Young, J.P., "Resonance Ionization Spectroscopy with Amplification,"... 

Resonance ionization spectroscopy is a photophysical process in which one electron can be removed from each of the atoms of a selected type. Since the saturated RIS process can be carried out with a pulsed laser beam, the method has both time and space resolution along with excellent (spectroscopic) selectivity. In a recent article [2] we showed, for example, that all of the elements except helium, neon, argon, and fluorine can be detected with the RIS technique. However, with commercial lasers, improved in the last year, argon and fluorine can be added to the RIS periodic table (see figure 2). 

G. Gerber By applying two-photon ionization spectroscopy with tunable femtosecond laser pulses we recorded the absorption through intermediate resonances in cluster sizes Na with n = 3,. 21. The fragmentation channels and decay pattern vary not only for different cluster sizes but also for different resonances corresponding to a particular size n. This variation of r and the fragmentation channels cannot be explained by collective type processes (jellium model with surface plasmon excitation) but rather require molecular structure type calculations and considerations. 

Resonance ionization spectroscopy (RIS) with pulsed tunable lasers offers new possibilities for constructing pulsed, highly selective ion sources with high efficiencies. Fig. 4 shows the principle of RIS and the planned set up. The efficiency of the ion source is determined mainly by the ratio of the repetition rate... 

Aniline clusters and the corresponding clusters with N2, CH4, CHF3 and CO are studied by detecting the depletion of resonance-enhanced multiphoton ionization spectroscopy (with time-of-flight mass spectrometer) which measures the vibrational spectra of the complexes. The interaction in clusters involving aniline cation is different from that of neutral aniline. The hydrogen bonding interaction is the main interaction in the aniline cation cluster, while neutral aniline clusters are due to van der Waals interaction. 

In atomic laser spectroscopy, the laser radiation, which is tuned to a strong dipole transition of the atoms under investigation, penetrates the volume of species evaporated from the sample. The presence of analyte atoms can be measmed by means of the specific interaction between atoms and laser photons, such as by absorption techniques (laser atomic absorption spectrometry, LAAS), by fluorescence detection (laser-induced fluorescence spectroscopy, LIFS), or by means of ionization products (electrons or ions) of the selectively excited analyte atoms after an appropriate ionization process (Figures lA and IB). Ionization can be achieved in different ways (1) by interaction with an additional photon of the exciting laser or of a second laser (resonance ionization spectroscopy, RIS, or resonance ionization mass spectrometry, RIMS, respectively, if combined with a mass detection system) (2) by an electric field applied to the atomization volume (field-ionization laser spectroscopy, FILS) or (3) by collisional ionization by surrounding atoms (laser-enhanced ionization spectroscopy, LEIS). 

The ionization potential of an element is one of its fundamental properties. It is known that the first ionization potential of heavy elements depends on relativistic effects. The Mainz group, in Germany, systematically determined the first ionization potential of the actinide elements from Ac through Es using laser spectroscopy as shown in Table 18.12 (Becke et al. 2002). O Figure 18.24 shows the comparison of ionization potentials between lanthanide and actinide atoms (Moore 1971 Becke et al. 2002). The atomic level structure of Fm (2.7 x 10 ° atoms) with a half-life of 20.1 h was studied for the first time by the method of resonance ionization spectroscopy. Two atomic levels were identified at wave numbers (25,099.8 0.2) cm and (25,111.8 0.2) cm (Sewtz et al. 2003). 

Figure lA. Resonance ionization spectroscopy is performed by monitoring molecular ions while tuning the laser wavelength. If the energy of one photon is in resonance with a neutral electronic excited state a second photon is able to be absorbed, giving rise to an ion current peak. Thus, the neutral UV-absorption spectrum is transferred to the ion current which can be recorded mass selectively (in opposition to the absorption). Thus UV spectroscopy and mass spectroscopy are combined as a two-dimensional technique. 

Figure 2.5 Schematics of the concepts for (a) ionization-loss stimulated Raman spectroscopy (ILSRS), where resonant two photon ionization of the molecular parent, follows the depletion of ground state reactant species as a result of SRS and (b) VMP, where preexcited molecules are dissociated and the ensuing H photofragments are probed by (2 -I-1) resonantly enhanced multiphoton ionization. Reproduced with permission from Ref. [86]. Copyright (2009) AIP Publishing LLC.

Very primary events in the chemical effect of radiations on matter are excitation and ionization of molecules, which result in the formation of neutral free radicals and radical ions. These reactive species play vital roles in the radiation-induced chemical reactions. As they are paramagnetic with an unpaired electron, electron spin resonance (ESR) spectroscopy has been a useful method for elucidating the mechanism of radiation-induced reactions in solid matter where radical species can be trapped temporarily. Since the early days of the chemical application of ESR, this method has been applied very often to the identification and quantification of free radicals in polymers irradiated by radiation [1]. This is probably because, from the view-point of fundamental research, a variety of free radicals are readily trapped in solid polymers and, from the view-point of applied research, these free radicals have close correlation with radiation-induced crosslinking and degradation of polymers. 

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