Laser-enhanced ionization

Vol. 136. Laser-Enhanced Ionization Spectrometry. Edited by John C. Travis and Gregory C. Turk... 

Photothermal Spectroscopy Methods for Chemical Analysis. By Stephen E. Bialkowski Element Speclatlon in Bioinorganic Chemistry. Edited by Sergio Caroli Laser-Enhanced Ionization Spectrometry. Edited by John C. Travis and Gregory C. Turk Fluorescence Imaging Spectroscopy and Microscopy. Edited by Xue Feng Wang and Brian Herman... 

Laser enhanced ionization spectroscopy and resonance ionization spectroscopy... 

Laser-enhanced ionization has also been observed by other workers and is sometimes called the opto-galvanic effect (10). 

Possible applications of laser enhanced ionization in flame diagnostics are 1. simultaneous observation of ionization and fluorescence signals from various levels might provide more information on the sequence of processes leading to and from the ionization continuum 2. the measurement of ion mobilities, relating to cross-sections for elastic collisions between ions and flame particles 3. measurement of ionization rate constants relating to cross-sections for inelastic collisions between excited atoms and other flame particles 4. measurement of recombination rate constants, relating to cross-sections for inelastic collisions between ions, electrons and neutrals. 

Consider first some of the factors affecting the design of such laser schemes. Ground electronic state based laser enhancement schemes [216, 3 366] rely on the induction of nuclear dipole moments to aid in promoting a desii reaction [30, 367], For example, the use of infrared (IR) radiation has been propoS to overcome reaction barriers on the ground electronic state [30, 367]. However proposal requires powers on the order of terawatts per centimeter sipis (TW/cm2). At these powers nonresonant multiphoton absorption, which irtvar leads to ionization and/or dissociation, becomes dominant, drastically reducin, yield of the reaction of interest. 

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). 

Laser-enhanced ionization (LEI) is one of a family of laser-induced ionization techniques which have been exploited for analytical spectrometry. The laser-induced ionization schemes which are important for flame spectrometry are illustrated in Fig. 1. 

Fig. 1. Laser-induced ionization schemes in flames. LEI-laser-enhanced ionization, DLI-dual laser ionization, MPI-multiphoton ionization...

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