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31.
Iodide salts of several N-retinylidenedialkylamines were prepared and their UV-VIS spectra recorded. Their lambda max values increased as the number of hydrogen atoms on the carbons alpha to nitrogen increased. In separate experiments, iodide salts of N-retinylidene-n-butylammonium (1) and N-retinylidene-n-butylmethylammonium (2) were prepared, and their excitation energies (delta E) were measured in selected solvents of varying dielectric constant (epsilon). Data from each compound gave a straight line which converged at epsilon = 0. On the other hand, when delta E values of the iodide and bromide of 2 were plotted vs solvent epsilon, parallel rather than convergent lines were obtained. When lambda max values of 1 and 2 were measured in a greater number of solvents, the solvents fell into four main groups. The first group, regular solvents, are rigid, have fixed dipoles, neither donate nor accept H-bonds, and the delta E of 1 and 2 decreases linearly as solvent epsilon increases. This line for 2 is taken as a standard against which other solvents are judged. A second class of solvents that are good H-bond donors like CHCl3, whose dipole moment coincides with the C-H bond axis, is located in an area below the standard line. A third group, nucleophilic solvents like tetrahydrofuran, whose dipole moment is coincident with a strongly nucleophilic oxygen atom are good H-bond acceptors and are found above the standard line. Solvents with unpredictable spectroscopic behavior are classed as anomalous. 相似文献
32.
S. Thomas E. Mohler F. Keilmann L. Genzel 《Applied Physics A: Materials Science & Processing》1984,33(4):247-250
We report changes in the excitonic absorption edge of CuCl caused by intense CO2 laser radiation at 10.6 m, a wavelength which lies in the infrared (ir) transparency region of CuCl. With an ir intensity of 0.4 GW/cm2 we observe a 100% absorption increase for the Kr+ laser probe wavelength of 406.7nm. The effect scales linearly with ir intensity but does not depend on relative polarization. We explain the effect by laser field induced electroabsorption of the exciton. The magnitude of the effect is closely related to electroabsorption induced by static external fields and by internal electric fields from optical phonons. 相似文献
33.
P E Blatz R H Johnson J H Mohler S K al-Dilaimi S Dewhurst J O Erickson 《Photochemistry and photobiology》1971,13(3):237-245
Abstract— –Preliminary examination of the effect of solution environment on the electronic absorption spectrum of N-retinylidene-n-butylamine(I) is reported. It is established that small amounts of CO2 dissolved in certain solvents cause the formation of the conjugate acid of I. This reaction is shown to be dependent on temperature and the concentration of CO2. The pKb of I in aqueous buffer was measured spectrophotometrically and found to be 8.71. Salts of I were prepared in a number of ways and their spectra were determined in selected solvents. The Λmax varies with method of preparation, and only one method gives reproducible results. The Λmnx is a function of the solvent in which the spectrum is determined. It was also found that the absorption maximum in wavenumbers is proportional to the negative logarithm of acid concentration. 相似文献
34.
Mohler DL Downs JR Hurley-Predecki AL Sallman JR Gannett PM Shi X 《The Journal of organic chemistry》2005,70(23):9093-9102
[Reaction: see text]. The photolysis of CpW(CO)3Me has been shown to produce methyl radicals and to cleave DNA in a single-stranded manner, and preliminary evidence implicated a carbon-centered radical in this process. In this work, the mechanism of strand scission in this reaction was determined to occur by hydrogen atom abstraction from the 4'- and 5'-positions of the deoxyribose moiety of the backbone of DNA. Additionally, in a side reaction that does not lead to frank strand scission, all four bases of DNA are methylated under these conditions; however, none of these base or backbone modifications lead to the formation of abasic sites. 相似文献
35.
H. Mohler H. Kühl O. Lüning St. Kovacz G. B. Pusrin G. Mueller E. Berliner K. Křtinský H. Annen E. A. Fisher P. Halten H. Stetter Natalie P. Kosmin B. Czyžewsky K. Ritter E. Elion J. de Vilmorin E. Cazaubon M. P. Neumann A. Schulerud O. Skovholt C. H. Bailey J. R. Nicholls W. Gründer A. H. M. Andreason C. O. Swanson E. B. Working W. F. Geddes R. K. Larmour Th. Ruemele J. Großfeld G. Kauert O. Fernández R. Folch K. Eble R. Bretschneider K. Mohs R. Viollier E. Iselin 《Analytical and bioanalytical chemistry》1934,97(11-12):435-450
36.
L. Benvegnin A. Jermstad O. Östby E. Monti de Astis F. Holzbach G. Amadio L. Paronetta A. A. Perazzo A. C. Arbrecchi R. Marcille P. Jaulmes L. Ferré P. Archinard L. Espil E. Capt C. Sumuleanu G. Ghimicescu M. V. Ionescu F. Konek E. Wettstein C. Béis E. Peynaud J. Schindler K. Kozák P. Berg G. Schulze A. Heiduschka H. Sommer H. Mohler Internationales Landwirtschaftsinstitut 《Analytical and bioanalytical chemistry》1938,115(3-4):148-158
37.
38.
Internationales Landwirtschaftsinstitut L. Benvegnin A. Jermstad O. Östby E. Monti de Astis F. Holzbach G. Amadio L. Paronetta A. A. Perazzo A. C. Arbrecchi R. Marcille P. Jaulmes L. Ferré P. Archinard L. Espil E. Capt C. Sumuleanu G. Ghimicescu M. V. Ionescu F. Konek E. Wettstein C. Béis E. Peynaud J. Schindler K. Kozák P. Berg G. Schulze A. Heiduschka H. Sommer und H. Mohler 《Fresenius' Journal of Analytical Chemistry》1938,115(3-4):148-158
Ohne Zusammenfassung 相似文献
39.
40.
Rönnburg KE Mohler E Roskos HG Ortner K Becker CR Molenkamp LW 《Physical review letters》2006,96(11):117203
Time-resolved optical spin-quantum-beat measurements performed on magnetically doped II-VI bulk semiconductors reveal an increase of the electron spin dephasing time with rising temperature typical for motional narrowing. With the dephasing being notably faster than in undoped II-VI semiconductors, the magnetic dopants must play a key role, modifying the known dephasing mechanisms and introducing new ones. Focusing on the latter, we theoretically explore the spin dephasing channel arising from magnetization fluctuations sampled by the itinerant excitons. This mechanism suffices to explain quantitatively the results of our time-resolved Faraday-rotation experiments on optically excited Cd(1-x)Mn(x)Te which we present here as a function of magnetic field, temperature and manganese dopant density. In addition to electron spin-quantum beats, some of our experiments reveal hole spin beats as well. 相似文献