Resonance ionization system

Adsorbed layers, thin films of oxides, or other compounds present on the metal surface aggravate the pattern of deactivation of metastable atoms. The adsorption changes the surface energy structure. Besides, dense layers of adsorbate may hamper the approach of metastable atom sufficiently close to the metal to suppress thus the process of resonance ionization. An example can be work [130], in which a transition from a two- to one-electron mechanism during deactivation of He atoms is exemplified by the Co - Pd system (111). The experimental material on the interaction of metastable atoms with an adsorption-coated surface of... 

Presolar grains are found in small quantities (with concentrations of ppb to several 100 ppm, see Table 2.1) in all types of primitive Solar System materials (Lodders Amari 2005 Zinner 2007). This includes primitive meteorites (the chondrites), IDPs, some of which might originate from comets, Antarctic micrometeorites (AMMs), and samples from comet Wild 2 collected by NASA s Stardust mission. Presolar grains are nanometer to micrometer in size. The isotopic compositions, chemistry, and mineralogy of individual grains with sizes >100 nm can be studied in the laboratory. Important analysis techniques are secondary ion mass spectrometry (SIMS) and resonance ionization mass spectrometry (RIMS)... 

Interestingly, there is a significant difference between the present tautomeric system and the ionizing systems of Section III.A.4 the barrier for the equilibrium reaction is substantially higher in the present case than in the previous systems, resulting in well resolved resonances for the hexa- and... 

Figure 1C. Periodic table depicting utility of RIMS, a. Elements for which resonance ionization feasibility has been demonstrated at NBS using thermal atomization b> elements for which ionization feasibility has been demonstrated in other laboratories using resonance ionization mass spectrometry (38-Ul> UU-32) c, elements for which isotope dilution RIMS have been achieved at NBS and d, potentially applicable for resonance ionization via two and three photon processes (Schemes 1, 2, and 5 of Figure U), using the BIMS system in Figure 6.

The recently introduced atmospheric-pressure laser ionization system (APLI) can be considered as a modification of APPI (Ch. 5.7.3). In APLI, the one-step photoionization of APPI is replaced by a two-photon process in resonantly-enhanced multi-photon ionization [148]. Enhanced response for polycyclic aromatic hydrocarbons (relative to APCI) was demonstrated. Molecular ions rather than protonated molecules are generated in APLI (cf. Ch. 6.5). 

Fig. 4 shows selected energy levels of the He /He systems. The Is3s4s state of He is situated just below the He (3 S) threshold. This state, which is excited with laser (O, rapidly autodetaches via the 2 Sks and 2 Pk.p channels. Following the decay, the residual He atom will be left in either the or 2 P excited states. Two different laser frequencies and a" were applied separately in the resonance ionization scheme used to monitor the population of the 2 8 and 2 states. The frequency 0)2 was chosen to induce a transition between the 2 S and the 24 P states of the He atom, when photodetachment into the 2 Sks channel was studied. The frequency co" induced a resonance transition between the 2 P and 26 D states of He, when photodetachment into the 2 Pkp channel was studied. The population of both the high lying Rydberg states were efficiently depleted by the electric field of the second quadrupole deflector and He+ ions thus produced were recorded as a function of frequency of laser m,. The output of laser w, was attenuated to avoid... 

AMS consists of a high-energy particle accelerator and an ion detector. Typical atom ratios for AMS isotope measurements are in the range of 10 10 to 10 15. These ratios fall well below the 1 to 10-9 range measured with other mass spectrometers, except for laser-based systems with resonance ionization techniques, which can match the range of the AMS. 

Gruning, C., Huber, G., Klopp, P., Kratz, J. V., Kunz, P., Passler, G., Trautmann, N., Waldek, A., and Wendt, K. 2004. Resonance ionization mass spectrometry for ultratrace analysis of plutonium with anew solid state laser system. Int J Mass Spectrom 235(2), 171-178. 

The Resonance Ionization Mass Spectrometry (RIMS) is a method to detect xenon and krypton with ultra high sensitivity using a laser technique [12] developed in collaboration with the University of Tokyo and Nagoya University. The block diagram of a RIMS system with a time of flight (TOF) mass spectrometer is illustrated in Fig. 15. 

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). 

Thanner, R. Oser, H. Grotheer, H.-H. Time-Resolved Monitoring of Aromatic Compounds in an Experimental Incinerator Using an Improved Jet-Resonance-Enhanced Multi-Photon Ionization System Jet-REMPI. Eur. Mass Spectrom. 1998,4,215-222. 

The control scheme that we have discussed does not require high-power lasers. The electric field of the light is weak enough that the levels of the system are not shifted by it. The laser induces transitions but these can be described as transitions between states of the free molecule. This is no longer the case when the laser is strong. The very potential on which the nuclei move can be altered by the external field because, if it is strong enough, its effect on the electrons can become comparable to the electrical field due to the nuclei or that of the other electrons. Once that happens a variety of other processes, such as non-resonant ionization,... 

The electric field of a laser is oscillating. Keldysh (Landau and Lifschitz, 1971) provided an estimate for the role of an oscillating field that is not resonant The Keldysh estimate for the onset of non-resonant ionization of an atom, for a field frequency lower than any natural frequency of the system, is consistent with our value of 10 W cm . Molecules are not like a hydrogen atom and, in particular, the gap between electronic states is very dependent on the intemuclear distances (Dietrich and Corkiim, 1992 Chelkowski and Bandrauk, 1995). This has interesting potential applications, e.g., S. Lochbrtmner et al.,... 

Substitution reactions by the ionization mechanism proceed very slowly on a-halo derivatives of ketones, aldehydes, acids, esters, nitriles, and related compounds. As discussed on p. 284, such substituents destabilize a carbocation intermediate. Substitution by the direct displacement mechanism, however, proceed especially readily in these systems. Table S.IS indicates some representative relative rate accelerations. Steric effects be responsible for part of the observed acceleration, since an sfp- caibon, such as in a carbonyl group, will provide less steric resistance to tiie incoming nucleophile than an alkyl group. The major effect is believed to be electronic. The adjacent n-LUMO of the carbonyl group can interact with the electnai density that is built up at the pentacoordinate carbon. This can be described in resonance terminology as a contribution flom an enolate-like stmeture to tiie transition state. In MO terminology,.the low-lying LUMO has a... 

When both reactants have comparable ionization potentials, there is a close relationship between the H2 and H2 transfer reactions. For instance, a low efficiency of the H. transfer reaction from the alkane to a neutral olefin molecule (at least in the case of cyclohexane) is paralleled by a low efficiency of the corresponding H2 transfer process. Such a relationship can be accounted for by resonance phenomena. Unfortunately, not enough information is available on those systems where the... 

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