Spectroscopy REMPI

Resonantly enhanced Multiphoton Ionization Spectroscopy, REMPI... 

Czech Republic). Development and application of semipermeable membrane devices (SPMDs) as environmental dosimeters for PCB contaminants in water, air, sediment, and soil is the subject of ongoing research by Huckins and Petty at Columbia Environmental Research Center in Missouri. Also at the Columbia Environmental Research Center, C. Orazio et al. are developing analytical methods for determining PCBs in environmental matrices. A reliable method for continuous monitoring of PCBs in incinerator stack gas emissions using resonance-enhanced multiphoton ionization spectroscopy in conjunction with time-of-flight mass spectroscopy (REMPI/TOFMS) is the topic of current research by... 

Vj = 1 <— v" = 1 transition will be at a different energy than the Vj = 0 <— v" = 0. We use this fact to measure the vibrational spectrum of V (OCO) in a depletion experiment (Fig. 12a). A visible laser is set to the Vj = 0 Vj = 0 transition at 15,801 cm producing fragment ions. A tunable IR laser fires before the visible laser. Absorption of IR photons removes population from the ground state, which is observed as a decrease in the fragment ion signal. This technique is a variation of ion-dip spectroscopy, in which ions produced by 1 + 1 REMPI are monitored as an IR laser is tuned. Ion-dip spectroscopy has been used by several groups to study vibrations of neutral clusters and biomolecules [157-162]. 

REMPI resonance-enhanced multiphoton ionization spectroscopy... 

This chapter deals mainly with (multi)hyphenated techniques comprising wet sample preparation steps (e.g. SFE, SPE) and/or separation techniques (GC, SFC, HPLC, SEC, TLC, CE). Other hyphenated techniques involve thermal-spectroscopic and gas or heat extraction methods (TG, TD, HS, Py, LD, etc.). Also, spectroscopic couplings (e.g. LIBS-LIF) are of interest. Hyphenation of UV spectroscopy and mass spectrometry forms the family of laser mass-spectrometric (LAMS) methods, such as REMPI-ToFMS and MALDI-ToFMS. In REMPI-ToFMS the connecting element between UV spectroscopy and mass spectrometry is laser-induced REMPI ionisation. An intermediate state of the molecule of interest is selectively excited by absorption of a laser photon (the wavelength of a tuneable laser is set in resonance with the transition). The excited molecules are subsequently ionised by absorption of an additional laser photon. Therefore the ionisation selectivity is introduced by the resonance absorption of the first photon, i.e. by UV spectroscopy. However, conventional UV spectra of polyatomic molecules exhibit relatively broad and continuous spectral features, allowing only a medium selectivity. Supersonic jet cooling of the sample molecules (to 5-50 K) reduces the line width of their... 

For chemical speciation, X-ray absorption spectroscopy is another supreme tool taking advantage of its electronic and structural information power. Also, REMPI-MS is outstanding in its selectivity for molecular species. Radioanalytical methods have also been used for speciation analysis [548]. Microscopical speciation analysis requires SSIMS or LMMS [549]. 

REMPI Resonance enhanced multiphoton Raman spectroscopy... 

Nir E, Muller M, Grace LI, de Vries MS (2002) REMPI spectroscopy of cytosine Chem Phys Lett... 

The general principle of detection of free radicals is based on the spectroscopy (absorption and emission) and mass spectrometry (ionization) or combination of both. An early review has summarized various techniques to detect small free radicals, particularly diatomic and triatomic species.68 Essentially, the spectroscopy of free radicals provides basic knowledge for the detection of radicals, and the spectroscopy of numerous free radicals has been well characterized (see recent reviews2-4). Two experimental techniques are most popular for spectroscopy studies and thus for detection of radicals laser-induced fluorescence (LIF) and resonance-enhanced multiphoton ionization (REMPI). In the photochemistry studies of free radicals, the intense, tunable and narrow-bandwidth lasers are essential for both the detection (via spectroscopy and photoionization) and the photodissociation of free radicals. 

The spectroscopy methods such as LIF and REMPI are utilized not only to detect the free radicals as discussed above, but also to directly measure the internal state distributions of the photoproducts in the photodissociation of free radicals. In this approach, the photochemistry is carried out in the free radical beam under single-collision conditions with well-defined... 

Further insights into the structural features of supersonically expanded molecular complexes is obtained using the REMPI spectroscopy. The supersonically... 

Hippier, M., and J. Pfab, Detection and Probing of Nitric Oxide (NO) by Two-Colour Laser Photoionisation (REMPI) Spectroscopy on the A <- X Transition, Chem. Phys. Lett., 243, 500-505 (1995). 

Tunable laser spectroscopic techniques such as laser-induced fluorescence (LIF) or resonantly enhanced multi-photon ionization (REMPI) are well-established mature fields in gas-phase spectroscopy and dynamics, and their application to gas-surface dynamics parallels their use elsewhere. The advantage of these techniques is that they can provide exceedingly sensitive detection, perhaps more so than mass spectrometers. In addition, they are detectors of individual quantum states and hence can measure nascent internal state population distributions produced via the gas-surface dynamics. The disadvantage of these techniques is that they are not completely general. Only some interesting molecules have spectroscopy amenable to be detected sensitively in this fashion, e.g., H2, N2, NO, CO, etc. Other interesting molecules, e.g. 02, CH4, etc., do not have suitable spectroscopy. However, when applicable, the laser spectroscopic techniques are very powerful. 

V. S. Letokhov In his exciting and dynamical report Prof. Schlag mentioned the historical development leading to ZEKE spectroscopy. Let me comment on this point. Laser-induced REMPI and ZEKE spectroscopies belong to the rich family of laser ionization spectroscopy techniques (Fig. 1) [1]. 

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