Absorption spectra studies

The hexahalorhenate(IV) anions have been the subjects of extensive electronic absorption spectra studies. Their spectra have been recorded in aqueous and non-aqueous solvents, in halide melts, in the solid state and doped into other crystal hosts (e.g. K2PtCl[Pg.172]

The absorption spectrum studies presented above merely reflect the electronic environment of the molecule and do not give specific information about the type of interaction. The data which must be accounted for in considering a physical mode for the binding process can be derived from several different approaches. Hydro-dynamic measurements on the DNA-drug complex are of interest, since Lerman58, S9 has established that an increase in the intrinsic viscosity of DNA and a decrease in the sedimentation coefficient of the polymer are two criteria for intercalation of ring systems between base pairs of a double-helical DNA. 

As one other example illustrating the power of symbolic mathematics programs. Fig. 6 shows a Mathematica calculation of Franck-Condon factors for the I2 B<— X electronic absorption spectrum studied in Exp. 39. These factors are the squares of the overlap integrals of the vibrational wavefunctions for the lower (v") and upper (v ) vibrational levels involved in a transition ... 

It should not be overlooked that physical-chemical studies so far undertaken yield only indirect evidence that positively charged protein groups combine with detergents. Direct evidence that the basic groups are involved is still wanting but may perhaps be obtained by absorption spectrum studies of the complexes. 

While a laser beam can be used for traditional absorption spectroscopy by measuring / and 7q, the strength of laser spectroscopy lies in more specialized experiments which often do not lend themselves to such measurements. Other techniques are connnonly used to detect the absorption of light from the laser beam. A coimnon one is to observe fluorescence excited by the laser. The total fluorescence produced is nonnally proportional to the amount of light absorbed. It can be used as a measurement of concentration to detect species present in extremely small amounts. Or a measurement of the fluorescence intensity as the laser frequency is scaimed can give an absorption spectrum. This may allow much higher resolution than is easily obtained with a traditional absorption spectrometer. In other experiments the fluorescence may be dispersed and its spectrum detennined with a traditional spectrometer. In suitable cases this could be the emission from a single electronic-vibrational-rotational level of a molecule and the experimenter can study how the spectrum varies with level. 

As a class the penicillins do not have a characteristic UV absorption spectrum. UV spectra did, however, play an important role in the structure elucidation of some of the penicillin degradation products during the early structure studies (B-49MI51104). 

When an ionic solution contains neutral molecules, their presence may be inferred from the osmotic and thermodynamic properties of the solution. In addition there are two important effects that disclose the presence of neutral molecules (1) in many cases the absorption spectrum for visible or ultraviolet light is different for a neutral molecule in solution and for the ions into which it dissociates (2) historically, it has been mainly the electrical conductivity of solutions that has been studied to elucidate the relation between weak and strong electrolytes. For each ionic solution the conductivity problem may be stated as follows in this solution is it true that at any moment every ion responds to the applied field as a free ion, or must we say that a certain fraction of the solute fails to respond to the field as free ions, either because it consists of neutral undissociated molecules, or for some other reason ... 

In the experiments descrihed above no tendency was found for the (ClOi)- ion to form a molecular ion by combination with Fe+++. The absorption spectrum characteristic of the Fe+++ ion in aqueous solution was therefore determined by studying solutions of FeC104 as a function of the hydroxyl-ion concentration. 

For long (infinite) /am.v-polyacclylene chains, the treatment of quantum lattice fluctuations is very complicated, because many lattice degrees of freedom couple in a non-linear way to the lowest electronic transitions. We have recently shown that for chains of up to 70 CH units, the amount of relevant lattice degrees of freedom reduces to only one or two, which makes it possible to calculate the low-energy part of the absorption spectrum in an essentially exact way [681. It remains a challenge to study models in which both disorder and the lattice quantum dynamics are considered. 

Nanosecond flash photolysis studies of Ct-nitronaphthalene in polar and nonpolar solvents led to the detection of the trip let-triplet absorption spectrum of this nitrocompd (Ref 26). 

The electronic spectrum of S2O has been studied both in absorption and in emission and both in the ultraviolet and the visible regions. The absorption spectrum in the near UV region is extremely intense and well suited to detect S2O in gases even at very low partial pressures. Two band systems are located in the UV region at 340-250 nm and at 230-190 nm [35] while a third system in the visible region at 645-575 nm was discovered only by op-toacoustic detection [36]. The 340-250 nm system has also been observed for matrix-isolated S2O [37]. For more details see [1, 38-47]. 

UV-vis spectra obtained for W0x-Zr02 samples, (NH4)6H2Wi204o, and bulk WO3 standards are shown in Figure 6. The absorption spectrum for (NH4)6H2Wi204o exhibits two bands with maxima at 4.9 and 4.0 eV. The band at 4.9 eV has been assigned to electron transfer from 0 to W in 0=W species, based on previous studies for MoOx samples [20]. The band at 4.0 eV probably reflects similar processes in W-O-W species. Individual bands are not apparent in bulk WO3 because of its polymeric nature and wide range of W-O-W distances. 

Kemp and coworkers employed the pulse radiolysis technique to study the radiolysis of liquid dimethyl sulfoxide (DMSO) with several amines as solutes [triphenylamine, and N, A, A, N -tetramethyl-p-phenylenediamine (TMPD)]. The radiolysis led to the formation of transient, intense absorptions closely resembling those of the corresponding amine radical cations. Pulse radiolysis studies determine only the product Ge, where G is the radiolytic yield and e is the molar absorption. Michaelis and coworkers measured e for TMPD as 1.19 X 10 m s and from this a G value of 1.7 is obtained for TMPD in DMSO. The insensitivity of the yield to the addition of electron scavenger (N2O) and excited triplet state scavenger (naphthalene) proved that this absorption spectrum belonged to the cation. 

Ito and Matsuda studied the y-radiolysis of 2-methyltetrahydrofuran (MTHF) solutions of diphenyl sulfone and dibenzothiophene-S,S-dioxide (DBTSD) at 77 K. They found that the radical anions of these sulfone compounds are formed and have intense absorption bands at 1030 nm and 850 nm, respectively. The blue glassy solution of y-irradiated diphenyl sulfone has absorption bands at both 1030 nm and 360 nm while the absorption spectrum of the benzenesulfonyl radical formed by UV irradiation of diphenyl sulfone solution at 77 K showed only a peak at 382 nm. Gamma-irradiated phenyl methyl sulfone solution showed an absorption band only at 385 nm. Consequently the appearance of the absorption bands in 800-1030 nm of diphenyl sulfone and DBTSD may suggest that the unpaired electron is delocalized on two phenyl rings. The same authors studied the radiolysis of MTHF solutions of disulfones (diphenyl and dihexyl disulfones). They found a blue coloring of the solution by the y-radiolysis of diphenyl disulfone and dihexyl disulfone due to absorption peaks at 695 nm and 690 nm respectively, besides smaller absorptions at 300-400 nm. Comparing these results to the previous observation, that phenyl methyl sulfone solution absorbs only at 398 nm, results in the conclusion that the absorption band at 690 nm is due to the linked two sulfone moieties. The authors found that substituents on the phenyl ring lead to shifts in the absorption maxima of the... 

The luminescence of macrocrystalline cadmium and zinc sulfides has been studied very thoroughly The colloidal solutions of these compounds also fluoresce, the intensity and wavelengths of emission depending on how the colloids were prepared. We will divide the description of the fluorescence phenomena into two parts. In this section we will discuss the fluorescence of larger colloidal particles, i.e. of CdS particles which are yellow as the macrocrystalline material, and of ZnS particles whose absorption spectrum also resembles that of the macrocrystals. These colloids are obtained by precipitating CdS or ZnS in the presence of the silicon dioxide stabilizer mentioned in Sect. 3.2, or in the presence of 10 M sodium polyphosphate , or surfactants such as sodium dodecyl sulfate and cetyldimethylbenzyl-ammonium... 

A surprising observation was made in the first experiments on the flash photolysis of CdS and CdS/ZnS co-colloids Immediately after the flash from, a frequency doubled ruby laser (X = 347.2 nm photon energy, = 3.57 eV) the absorption spectrum of the hydrated electron was recorded. This species disappeared within 5 to 10 microseconds. More recent studies showed that the quantum yield increased... 

In a pulse radiolysis study of solutions of CdS of different particle size, the rate of reaction of the OH radical with the colloidal particles was studied as well as the absorption spectrum of the products The hydroxyl radical reacts on its first encounter... 

Gratzel and Serpone and co-workers recently reported on a picosecond laser flash photolysis study of TiO. They observed the absorption spectrum immediately after the 30 ps flash and attributed it to electrons trapped on Ti" " ions at the surface of the colloidal particles. The absorption decayed within nanoseconds, the rate being faster as the number of photons absorbed per colloidal particle increased. This decay was attributed to the recombination of the trapped electrons with holes. 

Radiation chemical studies were carried out with an acidic WO3 H O sol stabilized by polyvinyl alcohol It was found that (CH3)2COH radicals inject electrons into the colloidal particles. A long-lived blue color arose and the absorption spectrum showed a rising absorption above 700 nm. This absorption could have been produced by free electrons, although it could not be ruled out that the electrons reduced ions... 

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