Solvent effects photoionization

A brief review and reassessment of data on the photophysics of benzene has been presented by Pereira. Evidence for the l E2g valence state has been obtained by u.v. two-photon spectroscopy.Slow electron impact excites fluorescence in thin films of benzene at 77 K as well as emission from isomers." The fluorescence yields and quenching by chloroform of alkyl-benzenes and 1-methylnaphthalene after excitation into Si, Sz, and S3 states and after photoionization have been measured. The channel-three process has been reconsidered in terms of the effects of local modes and Morse oscillator potentials. Excited-state dipole moments of some monosubstituted benzenes have been estimated from solvent effects on electronic absorption spectra, Structural imperfections influence the photochemistry of durene in crystals at low temperatures. Relaxation time studies on excited oxido-substituted p-oligophenylenes have been made by fluorescence depolarization... 

Another MPE procedure, well implemented for the ab initio description of the solute, has been elaborated by Mikkelsen et al. (1988). The method is limited to spherical cavities and it is used not for chemical reactions, but for the study of solvent effects on a number of properties of solutes at fixed geometry (electronic spectra, photoionization, hyperpolarizabilities) with results of remarkable interest (Agren et al., 1993 Mikkelsen et al., 1994). 

T. J. Kauppila, T. Kuuranne, E. C. Meurer, M. N. Eberlin, T. Kotiaho, and R. Kostiainen. Atmospheric Pressure Photoionization Mass Spectrometry Ionization Mechanism and the Effect of Solvent on the Ionization of Naphthalenes. Anal. Chem., 74(2002) 5470-5479. 

Robb, D. B., and Blades, M. W. (2005). Effects of solvent flow, dopant flow, and lamp current on dopant-assisted atmospheric pressure photoionization (DA-APPI) for LC-MS. Ionization via proton transfer.. Am. Soc. Mass Spectrom. 16, 1275—1290. 

In other polar solvents such as alcohols and acetonitrile (CH3CN) the ejected electron can be trapped as a solvated electron , shared between several solvent molecules, or as a negative ion by attachment to a solvent molecule. Many aromatic molecules such as naphthalene, anthracene, etc., undergo such photoionizations with low quantum yields. The ions eventually recombine on a time-scale of microseconds, and there is no overall chemical effect (Figure 4.6). 

The fluorescence polarization excitation spectrum has been measured for thymine in aqueous solution. " The depolarization at the red edge is attributed to the hidden n, ir transition. Ionization of the lowest excited singlet and triplet states have been determined by the effect of pH on the absorption, fluorescence, and phosphorescence spectra of purines and pyrimidines. " Spectral, polarization, and quantum yield studies of cytidylyl-(3, 5 )-adenosine have also been published. Intermediates in the room-temperature flash photolysis of adenine and some of its derivatives have been identified hydrated electron, radical cations and anions, and neutral radicals resulting from their reactions have been assigned. Photoionization occurs via the triplet state. FMN encapsulated in surfactant-entrapped water pools interacts with polar head groups, entrapped water molecules, and outer apolar solvent. ... 

Kauppila, T. J., Kuuranne, T., Meurer, E. C., Eberlin, M. N., Kotiaho, T., and Kostiainen, R., Atmospheric pressure photoionization mass spectrometry. Ionization mechanism and the effect of solvent on the ionization of naphthalenes. Anal. Chem., 74, 5470-5477, 2002. 

Mechanistic and product distribution differences between organic solvents, organized systems such as micelles, and water may be due to many causes, such as proximity effects due to differences in solvation, retardation or promotion of photoionization and other electron-transfer processes, concentration effects caused by increased solubility in one phase of a two-phase system, selective quenching or promotion effects by codissolved solutes, or other factors. 

Holroyd, R.A., and Russell, R.L., 19/4, Solvent and temperature effects in the photoionization of tetramethyl-p-phenylenediamine, J. Phys. Chem., 78 2128. 

Benzene 10 Highly toxic, profound CNS and bone narrow toxic effects, risks for leukemia In degreasing operations, printing, electronics and rubber manufacture, paints, solvents and intermediates for chemical synthesis 0.2 pg/1 by GC with photoionization detectimi and confirmation by MS... 

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