Search results for "absorption"
showing 10 items of 2701 documents
Determination of fluoride after direct separation from acid medium by collection of its volatile compounds
1989
A method is proposed for determination of fluoride by separation in acid medium followed by ion-selective electrode measurement. The separation is done at temperatures up to 200 °C, without any previous treatment of the sample, in a PTFE reactor designed to ensure the complete absorption of volatile fluoride compounds. The distillation variables (temperature, time and acid concentration) have been optimized and the interference of other various species in the separation step has been studied. The method has been applied to geological samples. The results obtained are statistically satisfactory.
TEMPERATURE DEPENDENCE OF THE OZONE ABSORPTION KINETICS IN AQUEOUS PHENOL SOLUTIONS
1978
(1978). TEMPERATURE DEPENDENCE OF THE OZONE ABSORPTION KINETICS IN AQUEOUS PHENOL SOLUTIONS. Chemical Engineering Communications: Vol. 2, No. 4-5, pp. 219-221.
Temperature and pH Dependence of Gd-DOTA and Gd-DTPA Complexes Dissociation Studied by EXAFS
1997
The Gd L3-edge of Gd(DTPA) 2- and Gd(DOTA) - complexes, in crystalline state and aqueous solutions presenting various pH (0.15-8) at different temperatures (25-90 °C), are investigated by XAFS experiments. For the Gd(DTPA) 2- . complexes we observe a strong pH (0.15-1.5) dependence of XAFS signals. On the other hand, the XAFS signals of Gd(DOTA) - complexes exhibit a light pH (1-1.5) dependence and for pH<1 we observe a ligand decomposition. Conceming both complexes, we note just a light temperature dependence. To obtain information about the short and medium range order (up to 5 A), multiple scattering calculation is performed. For the first coordination shell, we apply multi-shell fitting…
Localized states in wide-gap oxide glasses
1997
Localized states manifest themselves by light absorption at the optical gap of a glass and by luminescence excited there with Stoke's shift. They are created by the minority structural motifs of one or many structural modifications in which a material can exist, and which can provide electronic states absorption at the optical gap. Their wavefunctions overlapping determine the luminescence intensity dependence on the temperature [I(T)on the order of magnitude exp(- T/T 0 )] and power law (t -1 ) of luminescence decay kinetics, which include intra-center processes due to triplet-singlet transitions and recombination processes due to a tunnel and overbarrier transitions, as well as a fast com…
Evidence for reverse pathways and equilibrium in singlet energy transfers between an artificial special pair and an antenna
2013
A dyad, 1, built on an artificial special pair (bis(meso-nonyl)zinc(II)porphyrin), [Zn2], a spacer (biphenylene), a bridge (1,4-benzene), and an antenna (di-meso-(3,5-di(t-butyl)phenyl)porphyrin free base), FB, is prepared by Suzuki coupling and is analyzed by absorption and steady state, and time-resolved emission spectroscopy at 298 and 77 K. Using bases from the Förster theory, evidence for two pathways for S 1 energy transfer, FB* → [Zn2], and [Zn2]* → FB, along with their respective rates, k ET ( S 1)1 and k ET ( S 1)-1, are extracted from the comparison of the fluorescence decays monitored at the emission maximum. At 77 K, the unquenched (1.79 ([Zn2]) and 10.6 ns (FB)) and quenched c…
Red- and Blue-Shifts in Oligo(1,4-phenyleneethynylene)s Having Terminal Donor−Acceptor Substitutions
2004
Four series of oligo(1,4-phenyleneethynylene)s (OPEs), 1−4 (a−d), each having a terminal dialkylamino group as their electron donor, were prepared by applying Sonogashira−Hagihara reactions and a protecting group strategy. To study the influence that the push−pull effect has on the long-wavelength absorption, three of the four series of OPEs contain terminal acceptor groups (CN, CHO, NO2). Extending the conjugation (increasing the number of repeat units, n) lowers the energy E(n) of the electron transition in the purely donor-substituted series 1a−4a (bathochromic shift). This effect is superimposed in the push−pull series 1−4 (b−d) by the effect of the intramolecular charge transfer (ICT),…
Cation-induced self-assembly of an amphiphilic perylene diimide derivative in solution and Langmuir–Blodgett films
2015
Abstract A novel amphiphilic perylenetetracarboxylic diimide (PDI) derivative, N-(4′-benzo-15-crown-5-ether)-N-hexyl-1,7-di(4-tert-butyl-phenoxy)perylen-3,4,9,10-tetracarboxylic diimide (15C5PDI), has been synthesized and characterized. Dimerization of 15C5PDI is induced in CHCl 3 solution with the present of K + , resulting in the formation of the slipped co-facial J -aggregates, as revealed by absorption and fluorescence spectroscopies. Analysis of the surface pressure–area ( π – A ) isotherms and spectral change for the monolayer formed at the air/water interface, disclosed that 15C5PDI molecules adopted the H -type aggregation mode with a face-to-face configuration and edge-on orientati…
Konvergenz von Absorption und Fluoreszenz bei gekreuzt konjugierten Oligomeren aus Chalkon-Bausteinen
1999
The absorption and fluorescence spectra of two series of chalcone oligomers (1a–d) and (2a–d) are reported. Due to small or vanishing orbital coefficients (HMO calculation) within the cross-conjugated systems, the bathochromic shifts caused by the extension of the chains are modest. The effective conjugation lengths amount to 6 and 14 chalcone building blocks in the absorptions of the series 1 and 2. The convergence of the fluorescence bands is already reached in 1d and 2d with 4 and 8 enone units, respectively. Besides the uniform or alternate arrangement of the chalcone building blocks, the positions of the propoxy substituents show a considerable influence on the electronic transitions p…
Dielektrische Relaxation und aromatischer Bindungszustand der Amino- und Hydroxylgruppe
1965
Bei funf Wellenlangen im Bereich von 60 cm bis 7 mm wurde in benzolischer Losung bei 20 °C die dielecktrische Absorption von Benzolderivaten gemessen, die Amino- oder Hydroxylgruppen enthalten. Danach erfolgt die elektrische Dipolorientierung bei N, N'-Dimethylanilin, Diphenylamin und ver wandten Molekulen in der Art, das die drei Bindungen des Stickstoffs uber die ebene Anordnung hinweg umklappen. Ebenso kann auch das Relaxationsverhalten von Anilin beschrieben werden. Voraussetzung fur diese Inversion ist die mesomere Wechselwirkung zwischen dem Stickstoff und einem aromatischen ϕ-Elektronen-system. Dagegen ergeben die Meswerte keinen Hinweis darauf, das bei der Hydroxylgruppe auch eine s…
A new interpretation for the structure of the VN bands of ethylene
1971
Abstract Potential surfaces for CC stretch and CH2 twisting of ethylene obtained by the combined SCF CI method lead to the prediction that non-vertical transitions are responsible for the absorption maximum in the VN bands and that the broad diffuse nature of the spectrum in this region could well be caused by the proximity of two states of the same symmetry of the twisted molecule.