Resonance Raman spectroscopy photoionization

Brouwer and Wilbrandt have applied resonance Raman spectroscopy and calculations to questions of structure of amine radical cations [73]. Well-resolved Raman spectra of trialkylamine radical cations that are so short-lived that their electrochemical oxidation waves are irreversible may be obtained at room temperature in solution by photoionization and time-resolved detection. Comparison of the observed spectrum with calculations for various isomers provides a powerful method of answering structural questions. Density-functional calculations prove much easier to apply to open-shell species than Hartree-Fock calculations, which require cumbersome and expensive corrections to introduce suffieient electron correlation to eonsider questions like the charge distribution of disubstituted piperazine (1,4-diazacyclohexane) radical cations. The dimethyl- and diphenyl-substituted piperazine radical cations are delocalized, but charge is localized on one ArN unit of the dianisyl-substituted compound [73dj. 

Femtosecond photodissociation dynamics of nitroethane and l-nitropropane have been studied in the gas phase and in solution by resonance Raman spectroscopy, with excitation in the absorption band around 200 nm. At such short time-scales it is possible to detect changes in the two N-O bond lengths in the Franck-Condon region, prior to C-N bond cleavage. Photolyses of nitroalkanes at 193 nm have been monitored by photoionization of the fragments and time-of-flight mass spectrometry. Both C-N and N-O bond dissociation pathways are observed and, under the conditions of free jet expansion, primary products such as pentyl and hexyl radicals are stabilized and can be detected. 

A number of less commonly used analytical techniques are available for determining PAHs. These include synchronous luminescence spectroscopy (SLS), resonant (R)/nonresonant (NR)-synchronous scan luminescence (SSL) spectrometry, room temperature phosphorescence (RTP), ultraviolet-resonance Raman spectroscopy (UV-RRS), x-ray excited optical luminescence spectroscopy (XEOL), laser-induced molecular fluorescence (LIMP), supersonic jet/laser induced fluorescence (SSJ/LIF), low- temperature fluorescence spectroscopy (LTFS), high-resolution low-temperature spectrofluorometry, low-temperature molecular luminescence spectrometry (LT-MLS), and supersonic jet spectroscopy/capillary supercritical fluid chromatography (SJS/SFC) Asher 1984 Garrigues and Ewald 1987 Goates et al. 1989 Jones et al. 1988 Lai et al. 1990 Lamotte et al. 1985 Lin et al. 1991 Popl et al. 1975 Richardson and Ando 1977 Saber et al. 1991 Vo-Dinh et al. 1984 Vo- Dinh and Abbott 1984 Vo-Dinh 1981 Woo et al. 1980). More recent methods for the determination of PAHs in environmental samples include GC-MS with stable isotope dilution calibration (Bushby et al. 1993), capillary electrophoresis with UV-laser excited fluorescence detection (Nie et al. 1993), and laser desorption laser photoionization time-of-flight mass spectrometry of direct determination of PAH in solid waste matrices (Dale et al. 1993). 

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