Laser-induced ionization

Laser desorption and ionization laser-induced breakdown spectroscopy, matrix-assisted laser desorption and ionization, and aerosol time-of-flight mass spectrometry... 

REMPI Resonance-enhanced multi- Laser-induced ionization ... 

Heather R W and Julienne P S 1993 Theory of laser-induced associative Ionization of ultracold Na Phys.Rev. A 47 1887... 

Kim NJ, Jeong G, Kim YS, Sung J, Kim SK, Park YD (2000) Resonant two-photon ionization and laser induced fluorescence spectroscopy of jet-cooled adenine. J Chem Phys 113 10051... 

Fig. 1 Principles of UV laser-induced biphotonic ionization of DNA bases...

The advancement of the application of lasers in combination with the molecular beam technique has made a great impact in the understanding of primary photodissociation processes. For state-specific detection of small fragments, laser-induced fluorescence, multiphoton ionization, and coherent laser scattering have provided extremely detailed information on the dynamics of photodissociation. Unfortunately, a large number of interesting... 

The decay of benzene from the S2 state under collision-free condition has also been studied. J. P. Reilly and co-worker studied the nanosecond UV laser induced multiphoton ionization/fragmentation processes. The rate equation model was used for the simulation and the lifetime of the second excited singlet state was estimated to be 20 ps.19 More recently the... 

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. 

In order to record excitation spectra, the radical ions must first be thermalized to the electronic ground state, which happens automatically if they are created in condensed phase (e.g. in noble-gas matrices, see below). In the gas-phase experiments where ionization is effected by collision with excited argon atoms (Penning ionization), the unexcited argon atoms serve as a heat bath which may even be cooled to 77 K if desired. After thermalization, excitation spectra may be obtained by laser-induced fluorescence. 

DGE a AC AMS APCI API AP-MALDI APPI ASAP BIRD c CAD CE CF CF-FAB Cl CID cw CZE Da DAPCI DART DC DE DESI DIOS DTIMS EC ECD El ELDI EM ESI ETD eV f FAB FAIMS FD FI FT FTICR two-dimensional gel electrophoresis atto, 10 18 alternating current accelerator mass spectrometry atmospheric pressure chemical ionization atmospheric pressure ionization atmospheric pressure matrix-assisted laser desorption/ionization atmospheric pressure photoionization atmospheric-pressure solids analysis probe blackbody infrared radiative dissociation centi, 10-2 collision-activated dissociation capillary electrophoresis continuous flow continuous flow fast atom bombardment chemical ionization collision-induced dissociation continuous wave capillary zone electrophoresis dalton desorption atmospheric pressure chemical ionization direct analysis in real time direct current delayed extraction desorption electrospray ionization desorption/ionization on silicon drift tube ion mobility spectrometry electrochromatography electron capture dissociation electron ionization electrospray-assisted laser desorption/ionization electron multiplier electrospray ionization electron transfer dissociation electron volt femto, 1CT15 fast atom bombardment field asymmetric waveform ion mobility spectrometry field desorption field ionization Fourier transform Fourier transform ion cyclotron resonance... 

The laser induces instantaneous vaporization of a microvolume (called a plume), and a mixture of ionized matrix and analyte molecules is released into the vacuum of the ion source. The relationship between the laser irradiance, I ascn and the number of molecules formed, Gma di, is most peculiar. There exists a threshold irradiance, peculiar to each matrix, below which ionization is not observed. Above this level, the ion production increases in a very strong, nonlinear, manner (often Gma di grows as Ilaser is raised to the eighth power). 

The focus of this chapter has been on the synthesis of new catalysts by parallel and combinatorial methods. Another aspect important to the development of new catalysts by these methods is the screening of these large libraries. We will not attempt to cover this topic comprehensively but do feel it is necessary to summarize some of the approaches that have been taken. Methods for screening libraries can be divided into both serial and parallel methods. Generally, the serial methods are adaptations of standard methods that allow for rapid individual analysis of each member of a library. Serial approaches for the analysis of libraries can be as simple as use of an auto sampler on a GC or HPLC system or as advanced as laser-induced resonance-enhanced multiphoton ionization of reaction products above the head-space of a catalyst (16) or microprobe sampling MS (63). The determination of en-antioselectivity in catalysis is a particular problem. Reetz et al. (64) reported the use of pseudoenantiomers and MS in the screening of enantioselective catalysis while Finn and co-workers (65) used diastereoselective derivatization followed by MS to measure ee. 

Valuable findings on the electronic ground and excited states of clusters have been derived from laser-induced multi-photon ionization (MPl) investigations, such as laser-induced fluorescence (LIF) and REMPI. This latter technique is particularly promising since it enables mass selection of cluster species and their spectral and thermochemical characterization. The complex is excited from its electronic ground state from a photon and then ionized by a second photon of equal or different frequency, near threshold to avoid cluster fragmentation. ... 

Laser-induced multiphoton ionization and hole burning spectroscopy... 

CONTENTS Preface, Joseph Sneddon. Analyte Excitation Mechanisms in the Inductively Coupled Plasma, Kuang-Pang Li and J.D. Winefordner. Laser-Induced Ionization Spectrometry, Robert B. Green and Michael D. Seltzer. Sample Introduction in Atomic Spectroscopy, Joseph Sneddon. Background Correction Techniques in Atomic Absorption Spectrometry, G. Delude. Flow Injection Techniques for Atomic Spectrometry, Julian F. Tyson. 

J. Pfab, Laser-induced Uuorescence and ionization spectroscopy of gas phase species. In R.J.H. Clark, R.E. Hester (Eds.) Spectroscopy in Environmental Science, Wiley, New York, 1995. 

The pump and probe pulses employed may be subjected to a variety of nonlinear optical mixing processes they may be prepared and characterized by intensity, duration, spectral band width, and polarization. They may arrive in the reaction chamber at a desired time difference, or none. The probe pulse may lead to ionizations followed by detections of ions by mass spectrometry, but many alternatives for probing and detection have been used, such as laser-induced fluorescence, photoelectron spectroscopic detection, absorption spectroscopy, and the like. 

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. 

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