Spectroscopy resonance ionization, RIS

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... 

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). 

Resonance ionization spectroscopy (RIS) is based on resonance multistep excitation of high-lying levels of free analyte atoms and their subsequent ionization. Ionization may be caused by the photons of the final laser step (photoioniza-... 

As we have seen, collisions are important for the signal generation in LEI. In low-pressure experiments photoionization instead is the principal origin of the signal. The term Resonance Ionization Spectroscopy (RIS) is then frequently used. Several examples of opto-galvanic detection schemes for different atoms are shown in Fig.9.11. If multi-photon excitation of the atoms to be studied is used the technique is referred to as REMPI (REsonance Multi-Photon Ionization) spectroscopy. The selectivity of RIS and REMPI can be further enhanced by using a mass spectrometer to ana-... 

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). 

LEIS laser-enhanced ionization spectroscopy FILS field ionization laser spectroscopy RIS resonance ionization spectroscopy RIMS resonance ionization mass spectrometry... 

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