Spectroscopy resonance-enhanced multiphoton ionization

REMPI resonance-enhanced multiphoton ionization spectroscopy... 

Resonantly enhanced Multiphoton Ionization Spectroscopy, REMPI... 

Aniline clusters and the corresponding clusters with N2, CH4, CHF3 and CO are studied by detecting the depletion of resonance-enhanced multiphoton ionization spectroscopy (with time-of-flight mass spectrometer) which measures the vibrational spectra of the complexes. The interaction in clusters involving aniline cation is different from that of neutral aniline. The hydrogen bonding interaction is the main interaction in the aniline cation cluster, while neutral aniline clusters are due to van der Waals interaction. 

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... 

Bog Boggis, S.A., Dyke, J.M., Tabrizchi, M., Richter, R. Resonance enhanced multiphoton ionization spectroscopy of the NCI molecule E Rydberg states studied by 2-photon excitation from the a state. Mol. Phys. 97 (1999) 81-92. 

Cohen R, Brauer B, Nir E, Grace L, de Vries MS (2000) Resonance-enhanced multiphoton ionization spectroscopy of dipeptides. J. Phys. Chem. A 104 6351-6355... 

Tembreull, R. Sin, C. H. Pang, H. M. Lubman, D. M. Resonance enhanced multiphoton ionization spectroscopy for detection of azabenzenes in supersonic beam mass-spectrometry. Anal Chem. 1985, 57, 2911-2917. 

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. 

This section will focus on the stmcture and energetics of chiral molecular complexes studied with Fourier-transform IR (FT-IR), microwave, LIF, hole burning (HB), IR fluorescence dip spectroscopy, resonance-enhanced multiphoton ionization (REMPl Fig. 5), and RET spectroscopy. 

Figure 2.5 Schematics of the concepts for (a) ionization-loss stimulated Raman spectroscopy (ILSRS), where resonant two photon ionization of the molecular parent, follows the depletion of ground state reactant species as a result of SRS and (b) VMP, where preexcited molecules are dissociated and the ensuing H photofragments are probed by (2 -I-1) resonantly enhanced multiphoton ionization. Reproduced with permission from Ref. [86]. Copyright (2009) AIP Publishing LLC.

The photolysis of aromatic species with tetranitromethane in perfluoro alcohol solvent has been studied, in which the radical cations were observed by EPR spectroscopy.284 Photo-stimulated reaction of 1- and 2-haloadamantanes and 1,2- and 1,3-dihaloadamantanes with various carbanionic nucleophiles afforded products rationalized through an SrnI mechanism.285 286 Photolysis of the cycloadduct formed between a functionalized derivative of C6o and diazomethane has been shown to afford a pah of ling-opened structures (125) and (126) via a proposed biradical intermediate (127) (Scheme 19). The UV-photolytic fragments of /-butyl iodide (T and /-Bu ) have been ionized by resonance-enhanced multiphoton ionization for TOF mass spectro-metric analysis.287 A two-dimensional position-sensitive detector provided angular distribution and translational energy data. 

In addition to the IR, Raman and LIBS methods previously discussed, a number of other laser-based methods for explosives detection have been developed over the years. The following section briefly describes the ultraviolet and visible (UV/vis) absorption spectra of EM and discusses the techniques of laser desorption (LD), PF with detection through resonance-enhanced multiphoton ionization (REMPI) or laser-induced fluorescence (LIF), photoacoustic spectroscopy (PAS), variations on the light ranging and detecting (LIDAR) method, and photoluminescence. Table 2 summarizes the LODs of several explosive-related compounds (ERC) and EM obtained by the techniques described in this section. 

ADE = adiabatic detachment energies ESC A = electron spectroscopy for chemical analysis HOMO = highest occupied molecular orbitals MAES = metastable atom electron spectroscopy MIES = metastable ionization electron spectroscopy OAT = oxygen atom transfer PES = photoelectron spectra PEI = pulsed field ionization PIES = Penning ionization electron spectroscopy QM = quantum-mechanical REMPI = resonantly enhanced multiphoton ionization SC = semiclassical VDE = vertical detachment energies XPS = x-ray photoelectron spectroscopy ZEKE = zero electron kinetic energy Cp = cyclopentadienyl, Ph = phenyl, CeHs Tp =... 

Resonance-enhanced multiphoton ionization (REMPI) has proved to be a versatile ionization technique for MS offering a number of advantageous features in the field of chemical analysis. Since it makes use of substance-specific excited states for the ionization process, it involves UV spectroscopy of the molecule to be ionized. Thus, it enables ionization of preselected compounds, control of the degree of fragmentation and, for a large number of substances, a high ionization efficiency. These features require that the excited molecular state(s) involved in the REMPI process not be significantly depleted... 

Vibrational spectra of aniline/cyclohexane and aniline/benzene clusters investigated by infrared depletion spectroscopy with selective resonance—enhanced multiphoton ionization with time-of-flight mass spectrometry (REMPI-TOF mass spectrometry) show186 an... 

The spectroscopic methods are based on time-resolved pump-probe schemes where the collision-free regime is usually attained by using low pressure conditions. Application of various linear and non-linear laser techniques, such as LIF (laser-induced fluorescence), REMPI (resonant-enhanced multiphoton ionization) and CARS (coherent antistokes Raman spectroscopy) have provided detailed information on the internal states of nascent reaction products [58]. Obviously, an essential prerequisite for the application of these techniques is the knowledge of the spectroscopic properties of the products. 

Figure B2.3.8. Energy-level schemes describing various optical methods for state-selectively detecting chemical reaction products left-hand side, laser-induced fluorescence (LIF) centre, resonance-enhanced multiphoton ionization (REMPI) and right-hand side, coherent anti-Stokes Raman spectroscopy (CARS). The ionization continuum is denoted by a shaded area. The dashed lines indicate virtual electronic states. Straight arrows indicate coherent radiation, while a wavy arrow denotes spontaneous emission.

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