Iodine spectrum absorption

Fig. 23.—Absorption (--) and ORD spectra of the amylose-iodine spectrum. (Reprinted...

Sample Molecular weight X 10 C.L. fi-Amyl-olysis limit, % Iodine complex, absorption spectrum ... 

Figure B2.5.12 shows the energy-level scheme of the fine structure and hyperfme structure levels of iodine. The corresponding absorption spectrum shows six sharp hyperfme structure transitions. The experimental resolution is sufficient to detennine the Doppler line shape associated with the velocity distribution of the I atoms produced in the reaction. In this way, one can detennine either the temperature in an oven—as shown in Figure B2.5.12 —or the primary translational energy distribution of I atoms produced in photolysis, equation B2.5.35.

Worenine. This alkaloid, also obtained by Kitasato from Coptis japonica was isolated as the tetrahydro-base, C,oHjg04N, which crystallises from alcohol in colourless prisms, m.p. 212-3°, and is oxidised by iodine in alcohol to worenine iodide, yellow crystals from which worenine chloride, thin orange-yellow prisms, m.p. 295° (dec.), can be obtained. Tetrahydro-worenine behaves as a tertiary base, contains methylenedioxy- but no methoxyl groups, and its absorption spectrum closely resembles that of tetrahydrocoptisine from which it differs in empirical composition by. CHj. Worenine is, therefore, represented by (XXX), the alternative position (a) for the methyl group being untenable, since a-methyltetra-hydrocoptisine obtained by Freund s method is not identical with... 

Figure 23. In situ X-ray absorption spectrum for half a monolayer of copper underpotentially deposited on a bulk Pt (111) electrode pretreated with iodine.

Soon after Dennison had deduced from the specific-heat curve that ordinary hydrogen gas consists of a mixture of two types of molecule, the so-called ortho and para hydrogen, a similar state of affairs in the case of iodine gas was demonstrated by direct experiment by R. W. Wood and F. W. Loomis.1 In brief, these experimenters found that the iodine bands observed in fluorescence stimulated by white light differ from those in the fluorescence excited by the green mercury line X 5461, which happens to coincide with one of the iodine absorption lines. Half of the lines are missing in the latter case, only those being present which are due to transitions in which the rotational quantum number of the upper state is an even integer. In other words, in the fluorescence spectrum excited by X 5461 only those lines appear which are due to what we may provisionally call the ortho type of iodine molecule. 

Measure the molecular absorption spectrum in the visible region (400 to 700 nm) of each of the standards. Also measure the molecular absorption spectrum of the heptane layer in the separatory funnel (the extract). You can fill the cuvette conveniently by using a dropper to draw the solution (top layer) out of the separatory funnel. Obtain the maximum absorbance for each and create the standard curve. Determine the concentration of iodine in the extract. 

Figure 21.4 Absorption spectrum of Iodine in a nonpolar and polar solvent.

A classic example of CT complex formation occurs in the solution of iodine (an acceptor) in cyclohexene (a donor), when the solution assumes a brown color due to a shift in its absorption spectrum. The brown is not a color in the physical sense, but rather the result of a very broad absorption band encompassing about 200 nm in the visible spectrum and evolving as a result of electronic changes in the CT complex. In contrast, a solution of iodine in CCI4—an inert solvent—is purple. 

The Electronic Absorption Spectrum of Molecular Iodine A New Fitting Procedure for the Physical Chemistry Laboratory 170... 

Blandamer et al (1964) pointed out that the absorption spectrum of iodine ions (I ) in NH3 has its maximum at Jtv=4.0eV the difference from that for an electron in a cavity, 4.0-0.8= 3.2eV, corresponds well to the electron affinity of iodine. In water the maxima for both I and a solvated electron are shifted by 0.8 eV to higher frequencies we deduce that the energy of the bottom of the conduction band in water is about 0.8 eV. 

The iodine was removed from the reaction mixtures by vacuum sublimation and subsequently identified by its characteristic spectrum in pyridine solution. A solution of the sublimate from these reaction products gave an absorption maximum at 369 m/jL, while a solution prepared by dissolving elemental iodine in pyridine produced an absorption band of similar shape with a maximum at 370 m. ... 

A spectrum of the color reaction of glycogen with iodine is recorded. The wavelength of the absorption maximum is positively correlated with the outer chain length of glycogen (i.e., the chain length distal of the branching points) [24]. 

The compound [PPN]2[Os6(CO)18] is insoluble in hydrocarbons, sparingly soluble in methanol, and very soluble in acetone, acetonitrile, dichlorometh-ane, and chloroform to give solutions that are stable indefinitely at room temperature. Its IR spectrum in CH2C12 exhibits an intense v(CO) absorption at 1991 and very weak absorptions at 1964, 1938, and 1910cm-1. The compound is easily oxidized back to Os6(CO)18 by treatment of a CH2C12 solution with iodine /2.n... 

S. Landau and E. Stenz examined the effect of low temp, and dissociation on the fluorescence of iodine vapour at low press. Fluorescence decreases as the temp, is raised, but does not cease at 800°. Dissociation destroys both fluorescence and the resonance spectra. It is therefore inferred that the complex vibrating system is not inherent in the atom, but in the molecule that the structure of the atom is relatively simple and that, in all probability, the absorption lines which are so characteristic of diatomic iodine and so sensitive to the action of monochromatic light, do not belong to the absorption spectrum of monatomic iodine. 

The absorption spectrum of the violet soln. is not very different from that of iodine vapour, although one is a band and the other a line spectrum. In his Handbuch der Spectroscopie (Leipzig, 1905), H. Kayser thus summarizes the observations on the absorption spectra of red and brown soln. of iodine ... 

The absorption spectrum of violet soln. is but little influenced by the nature of the solvent, by the temp, or by the concentration of the soln. With brown soln. of the same concentration, the absorption in the violet end of the visible spectrum and in the ultraviolet is much more marked. H. Gautier and G. Charpy, E. Wiedemann, and H. Ebert explain the peculiarities in the optical properties of iodine soln. by assuming a polymerization of the solute iodine which in the violet soln. contain I2-molecules, and in the brown soln. In+2-molecules. Under any particular set of conditions, there is a state of equilibrium In+2 wl2, which determines the tint of the soln. From measurements of the raising of the vap. press, of iodine in solvents which produce brown and violet soln., M. Loeb assumed that the iodine in the brown soln. is present as I4 molecules and in the violet soln. as I2 molecules. He explained the change from brown to violet with a rise of temp, by assuming that the equilibrium I4 2I2 is displaced in favour of the I2 molecules, and conversely with a lowering of the temp. 

J. J. van Laar has shown how the form of the vap. press, curves of a liquid mixture can furnish an indication, not a precise computation, of the degree of dissociation of any compound which maybe formed, on the assumption that the different kind of molecules in the liquid—12, Br2, and IBr—possess partial press, each of which is equal to the product of the vap. press, of a given component in the unmixed state and its fractional molecular concentration in the liquid. It is assumed that in the liquid, there is a balanced reaction 2IBr I2-)-Br2, to which the law of mass action applies, where K is the equilibrium constant, and Clt C2, and C respectively denote the concentration of the free iodine, free bromine, and iodine bromide. From this, P. C. E. M. Terwogt infers that at 50 2°, K for the liquid is 7j and that for iodine monobromide about 20 per cent, of the liquid and about 80 per cent, of the vapour is dissociated. That the vapour of iodine monobromide is not quite dissociated into its elements is evident from its absorption spectrum, which shows some fine red orange and yellow lines in addition to those which characterize iodine and bromine. In thin layers, the colour of the vapour is copper red. 0. Ruff29 could uot prove the formation of a compound by the measurements of the light absorption of soln. of iodine and bromine in carbon tetrachloride. 

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