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Solvent dependence of the first hyperpolarizability of p-nitroanilines: Differences between nonspecific dipole–dipole interactions and solute–solvent H-bonds (1998)

Huyskens, François L.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 108 (1998), S. 8161-8171

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: In this paper, the influence of solvents on the first hyperpolarizability β of nonlinear optical (NLO) molecules is studied at 25 °C for solutions of p-nitroaniline and N,N-dimethyl paranitroaniline in some 50 solvents belonging to different classes. The hyperpolarizabilities deduced from measured hyper-Rayleigh scattering are the relative ones with as reference that of paranitroaniline in 1,4-dioxane. Taking for the latter the literature value of 16.9 10−30 esu, the β values vary from 14.4 to 29.9 10−30 esu for paranitroaniline and from 28.7 to 46.2 10−30 esu for N,N-dimethyl paranitroaniline. A selection of the solvents is made on the basis of the fraction of the time γ0 during which the NLO molecule is not involved in H-bonding with the solvent molecules. γ0 can be determined from the solubility in the given solvent. The formation of specific solute–solvent interactions as H-bonds always increases the hyperpolarizability β. In the absence of such interactions, the hyperpolarizability increases with the square root of the gaseous dipole moment of the solvent molecule and decreases when the mean interdistance between the center of the NLO molecule and the closest solvent dipole increases. A statistical study of a large number of solvents leads indeed to the correlation β=βgas+aμS/VS where a is a constant for a given NLO molecule. When H-bonds are formed the correlation becomes: β=βgas+γ0aμS/VS+(1−γ0)bμS, where b is a constant for a given NLO molecule. H-bond formation enhances the hyperpolarizability because it reduces the distance between the neighboring solvent dipole and the center of the NLO molecule to a constant value, independent of VS. © 1998 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.476171

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Nonlinear dynamics of feedback modulated magnetic islands in toroidal plasmas (2000)

Fitzpatrick, Richard ; Waelbroeck, François L.

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 7 (2000), S. 4983-4995

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ISSN: 1089-7674

Source: AIP Digital Archive

Topics: Physics

Notes: An analysis is presented of the dynamics of a helical magnetic island chain embedded in a toroidal plasma, in the presence of an externally imposed, rotating, magnetic perturbation of the same helicity. Calculations are carried out in the large aspect-ratio, zero-β, resistive magnetohydrodynamical limit, and incorporate a realistic treatment of plasma viscosity. There are three regimes of operation, depending on the modulation frequency (i.e., the difference in rotation frequency between the island chain and the external perturbation). For slowly modulated islands, the perturbed velocity profile extends across the whole plasma. For strongly modulated islands, the perturbed velocity profile is localized around the island chain, but remains much wider than the chain. Finally, for very strongly modulated islands, the perturbed velocity profile collapses to a boundary layer on the island separatrix, plus a residual profile which extends a few island widths beyond the separatrix. Analytic expressions are obtained for the perturbed velocity profile, the island equation of motion, and the island width evolution equation in each of these three regimes. The ion polarization correction to the island width evolution equation, which has previously been reported to be stabilizing, is found to be destabilizing in all three regimes. © 2000 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.1318360

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Regioselectivity of dechlorination of DDT and its metabolites in mass spectrometry (1995)

Lépine, François L. ; Milot, Sylvain ; Mamer, Orval A.

Chichester : Wiley-Blackwell

Biological Mass Spectrometry 30 (1995), S. 885-892

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ISSN: 1076-5174

Keywords: Chemistry ; Analytical Chemistry and Spectroscopy

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Physics

Notes: DDT and several of its metabolites were synthesized with their aromatic chlorines enriched with 37Cl. The mass spectra of these compounds were recorded under electron impact and under methane positive-ion and electroncapture negative-ion chemical ionization. The regioselectivity of the dechlorination reactions was determined by measurement of the relative proportions of the unlabeled aliphatic versus the labeled aromatic chlorines in the various fragment ions observed. For all the α,β-unsaturated compounds studied under electron impact ionization, the regioslectivity is small, as both the aromatic and the aliphatic chlorines are lost. Under positive-ion chemical ionization, the dechlorination is highly regioselective, the aliphatic chlorines being almost exclusively lost. Under electron-capture negative-ion chemical ionization, the regioselectivity is also very high and the reactivity of the various chlorines is often controlled by the position of the aromatic chlorines.

Additional Material: 4 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/jms.1190300614

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Dechlorination of polychlorinated biphenyls in electron impact mass spectrometry: Regioselective analysis using 35Ci-labelled compounds (1992)

Lépine, François L. ; Milot, Sylvain M. ; Reimer, Mark L. J. ; [et al.]

Chichester : Wiley-Blackwell

Biological Mass Spectrometry 27 (1992), S. 1311-1316

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ISSN: 0030-493X

Keywords: Chemistry ; Analytical Chemistry and Spectroscopy

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Notes: Four tetrachlorinated bipbenyls were chlorinated with 35Cl2 to yield seventeen polychlorinated biphenyls (PCBs) substituted once or twice with chlorine enriched in 35Cl. Gas chromatographic analysis of the mixtures allowed the identification of the labelled PCBs produced by comparison of their relative retention times with published values. This also permitted the assignment of the position of the labels in these molecules. Mass spectrometric determination of the 35Cl/35Cl ratio of the ions corresponding to successive dechlorination of these PCBs in positive-ion electron impact (EI) allowed quantification of the residual 35Cl label in these ions. Chlorines in the ortho position are lost preferentially to those in meta or para positions. The first dechlorination reaction was found to be totally regioselective for at least two PCB congeners.

Additional Material: 1 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/oms.1210271127

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Dechlorination of polychlorinated biphenyls in electron-capture negative-ion chemical ionization mass spectrometry (1994)

Lépine, Francois L. ; Milot, Sylvain M. ; Reimer, Mark L. J. ; [et al.]

Chichester : Wiley-Blackwell

Biological Mass Spectrometry 29 (1994), S. 133-142

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ISSN: 0030-493X

Keywords: Chemistry ; Analytical Chemistry and Spectroscopy

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Notes: The electron-capture negative-ion chemical Ionization mass spectra of 36 35Cl mono- and di-labelled penta- and hexachlorobiphenyls were studied. Under the conditions of the analyses, the dechlorination of these congeners probably proceeds through electrophilic hydrogen atom attachment followed by rapid loss of the chlorine atom at the same position. These dechlorination reactions occur regioselectively. When present, ortho-chlorines are lost preferentially to meta- and para-chlorines. The extent of the dechlorination reaction, as seen by the relative abundance of the [MH — Cl]- ions, decreases with increasing number of ortho-chlorines.

Additional Material: 8 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/oms.1210290304

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