Studies of phase transformations in nitrates and nitrites II. Changes in ultra-violet absorption spectra accompanying thermal transformations in the crystals

1963 ◽  
Vol 276 (1367) ◽  
pp. 453-460 ◽  
Keyword(s):  
Phase Transformations ◽  
Absorption Spectra ◽  
Alkali Metals ◽  
Ultra Violet ◽  
Crystal Form ◽  
Potassium Nitrate ◽  
Thermal Transformations ◽  
Absorption Bands ◽  
Potassium Nitrite ◽  
Cyclic Changes

Changes in ultra-violet absorption spectra have been measured for nitrates and nitrites of the alkali metals and for ammonium, silver and thallous nitrates, in relation to thermal transformations in these solids. A gradual shift of absorption bands is found to accompany thermal expansion of all the crystals. More abrupt changes in absorption spectra are observed at transformation points from one crystal structure to another; in many instances these two effects of temperature can be correlated. In cases where crystal structures are known, shifts in absorption maxima due to changes in temperature have been interpreted. in relation to changes in the distances between cations and anions. By means of the techniques described, ultra-violet absorption spectroscopy provides a sensitive means for studying various thermodynamic effects in phase transformations. Thus with ammonium nitrate, hysteresis with both superheating and supercooling is observed for the transitions IV ^ III ( T c ~ 32 °C) and III ^ II ( T c ~ 88 °C), but not II ^ I ( T c ~ 125 °C). With potassium nitrate during cyclic changes of temperature a (metastable) crystal form III appears. With potassium nitrite, a new crystal transformation showing hysteresis ( T c ~ 40 °C) is readily detected by ultra-violet spectroscopy.

scholarly journals The absorption spectra of conjugated dienes in the vacuum ultra-violet (1)

1940 ◽  
Vol 174 (957) ◽  
pp. 220-234 ◽  
Keyword(s):  
Absorption Spectrum ◽  
Absorption Spectra ◽  
Electronic Structures ◽  
Spectroscopic Data ◽  
Ultra Violet ◽  
Conjugated Dienes ◽  
Strong Absorption ◽  
Absorption Bands ◽  
Lennard Jones ◽  
Vacuum Ultra Violet

Butadiene is important as the simplest example of resonance between two conjugated double bonds. The comparison of its ultra-violet absorption spectrum with that of ethylene might be expected to give some indication of the way the π electrons of the molecule are affected by the resonance. The electronic structures of a number of molecules for which resonance is important have been worked out theoretically by Hückel (1935), Lennard- Jones (1937), Sklar (1937) and Mulliken (1939 a and b ). The purpose of the present work is to obtain spectroscopic data with which the theoretical expectations can be compared. As most of the strong absorption bands of these molecules occur at wave-lengths less than 2000 A, the investigation falls naturally into the region of vacuum spectroscopy.

scholarly journals The absorption spectrum of formic acid in the vacuum ultra-violet

1937 ◽  
Vol 162 (908) ◽  
pp. 110-120 ◽  
Keyword(s):  
Electronic Structure ◽  
Formic Acid ◽  
Absorption Spectra ◽  
Ultra Violet ◽  
The Body ◽  
Hydrogen Atoms ◽  
Absorption Bands ◽  
Additional Absorption ◽  
Lyman Continuum ◽  
Vacuum Ultra Violet

Absorption spectra in the far ultra-violet region of the spectrum have recently assumed an important role in fixing the electronic structures of polyatomic molecules. This has been especially true of organic molecules such as acetylene, ethylene, the alkyl halides, alcohols, ethers and ketones. While all “molecular electrons” (i. e. those not contained in inner shells) can be expected to give rise to absorption bands in the region 2000–1000 A, it most frequently happens that one special electron type dominates the absorption. For example, the excitation of non-bonding pπ electrons dominate the absorption of methyl and ethyl iodides (Price 1936 a ); so-called “lone pairs” located on the oxygen atoms are responsible for all the strong bands of water, formaldehyde, etc. (Mulliken 1935 a, b ; Price 1935 a , 1936 b ). In order to obtain discrete absorption bands, which are desirable for the purposes of interpreting electronic structure, it is usually necessary to take the very simplest organic molecule containing the group we wish to study. Thus for molecules of the type R 1 COO R 2 ( R being an alkyl group or a hydrogen atom) it has been found that only the simplest of these, namely formic acid, shows discrete absorption bands. The interpretation of the electronic structure of the carboxyl group will therefore depend to a considerable extent upon the analysis of these discrete bands. From the discussion which follows it will be easy to see why the continuous absorption from the larger molecules of the type R 1 COO R 2 follows roughly the envelope of the discrete absorption of HCOOH except in so far as it is enhanced in certain regions by additional absorption from C—C and C—H bonding electrons or suffers small shifts to longer wave-lengths as a result of the substitution of hydrogen atoms by alkyl groups. The experimental technique employed in obtaining absorption spectra in the vacuum ultra-violet has been described elsewhere (Collins and Price 1934). The Lyman continuum serves as the background against which the 19340. The Lyman continuum serves as the background against which the absorption is observed, and the gas under investigation is allowed to flow continuously through the body of the spectrograph.

Studies of phase transformations in nitrates and nitrites I. Changes in ultra-violet absorption spectra on melting

1963 ◽  
Vol 276 (1367) ◽  
pp. 437-452 ◽  
Keyword(s):  
Nitric Acid ◽  
Phase Transformations ◽  
Ammonium Nitrate ◽  
Absorption Spectra ◽  
Ultra Violet ◽  
The Other ◽  
Sodium Potassium ◽  
Nearest Neighbours ◽  
Isopropyl Nitrate ◽  
Sodium And Potassium

Ultra-violet absorption spectra of ions in crystals are sensitive to their environment of neighbouring ions. This fact is utilized to study melting processes in nitrates and nitrites, with particular reference to changes in the average shell of nearest neighbours around any ion, on passing from crystal to melt. For the nitrates of sodium, potassium, rubidium, caesium, thallium and silver, for ammonium nitrate and for the nitrites of sodium and potassium this shell appears to contract on melting, which is attributed to the formation of association complexes in the melt. For the two crystal hydrates HNO 3 . H 2 O and HNO 3 . 3H 2 O, corresponding changes are observed, suggesting that the structure and absorption spectra correspond with the ions (OH 3 )+ and NO - 3 in the crystals, likewise giving rise to tighter association complexes on melting. Pure nitric acid on the other hand behaves in a manner more closely similar to isopropyl nitrate.

scholarly journals Internal photoelectric absorption in halide crystals

1933 ◽  
Vol 141 (843) ◽  
pp. 209-215 ◽  
Keyword(s):  
Absorption Spectra ◽  
Ultra Violet ◽  
Alkali Halides ◽  
Lattice Points ◽  
Wave Functions ◽  
Absorption Bands ◽  
Progressive Change ◽  
Periodic Field ◽  
The Right ◽  
Insulating Properties

The possession of absorption bands in the ultra-violet by otherwise transparent crystals has been recognized for a long time as determining the dispersion of the medium. This absorption of radiation is one which produces no progressive change in the crystal. On the other hand, the illumination of crystals which gives rise to photochemical and photo-conduction phenomena causes a progressive change in the crystal and consequently in its absorption spectrum. Measurements have recently been made of the original and induced absorption spectra of many photo-conducting crystals, in the hope of elucidating the formation of the latent photographic image. 1. Quantum mechanics gives us entirely new ideas as to how to correlate the absorption spectra of crystals with their insulating properties. Both phenomena are alike concerned with the quantized electron levels of the crystal. These allowed levels belong not to individual atoms or ions but to the crystal as a whole. The wave functions representing the valence electrons are not localized at individual lattice points, but are oscillatory throughout the crystal. Even in an insulator they are the wave functions of an electron gas moving in the periodic field of the lattice. The opacity of a metal for all wavelengths from the infra-red far into the ultra-violet is due to the fact that electron transitions are possible to vacant levels of all higher energies. For other pure crystals, however, the allowed bands of levels are broken up by wide zones of disallowed energies; and it is these zones which at the same time give to a crystal the properties both of transparency to light and non-conduction to electric current. More exactly, these properties are due to the fact that a, zone of forbidden energies divides a band of levels, which at low temperatures is completely filled with electrons, from a similar higher band which is completely empty. For crystals which are transparent to all visible light we can at once say that the width of this particular zone must be more than 3 ε-volts; for the alkali halides which are transparent into the Schumann region it must be at least more than 5 or 6 ε-volts. When illuminated with ultra-violet light of the right wave-lengths, however, such a crystal is almost on a par with a metal; it contains as many electrons, and the levels are similar; over narrow regions in the ultra-violet, therefore, it absorbs as if it were a conductor and shows selective metallic reflection. The theory of the insulating properties of these crystals has been discussed by A. H. Wilson. The same scheme of levels must be used for correlating conductivity with opacity, and insulation with transparency in the case of liquids, such as mercury and water.

scholarly journals The absorption spectra of mixed metallic vapours

1924 ◽  
Vol 105 (730) ◽  
pp. 221-225 ◽  
Keyword(s):  
Absorption Spectra ◽  
Alkali Metals ◽  
Molecular Form ◽  
Band Spectrum ◽  
Absorption Bands ◽  
Metal Vapour ◽  
Sodium Potassium ◽  
Physical Conditions ◽  
Sodium And Potassium ◽  
Great Complexity

It has been known for many years that bands of great complexity occur in the absorption spectra of the alkali metals. The extensive absorption bands of sodium vapour in the green and red portions of the spectrum have, in particular, attracted considerable attention. R. W. Wood has discussed fully the structure of these bands, the manner in which they fluctuate with change in certain physical conditions, and their connection with the fluorescence spectrum. The existence of these bands leads to the conclusion that a certain number of the atoms in an alkali metal vapour are associated, though other considerations have indicated that the proportion present in the molecular form cannot be large. It is reasonable to suppose that, in a mixture of the vapours of two alkali metals, "mixed" molecules containing atoms of both elements will "exist" molecules containing atoms of both elements will exist, in addition to these normally present in the unmixed vapours. These "mixed" molecules if present in sufficient number will exhibit an absorption spectrum, probably similar in character to the bands of the simple alkali metals. In the present communication a new band spectrum is described which is developed only in the vapour of mixtures of sodium and potassium and which, it is suggested, is produced by the sodium-potassium molecules present in the mixed vapour.

scholarly journals The ultra-violet absorption spectra of blood sera

1916 ◽  
Vol 89 (617) ◽  
pp. 327-335 ◽  
Keyword(s):  
Clinical Practice ◽  
Absorption Spectra ◽  
Scientific Research ◽  
Ultra Violet ◽  
Research Fund ◽  
Absorption Bands ◽  
Pale Yellow ◽  
New Instrument ◽  
Visible Spectra ◽  
Derivatives Of

At the end of the year 1913 there was introduced a new kind of sector spectrophotometer designed especially for investigation of the ultra-violet spectrum. The possibility of applying the new instrument to the furtherance of medical and physiological science was soon appreciated by the author, and in conference with Dr. C. E. Wheeler it was decided that a study of the ultra-violet absorption spectra of blood sera might lead to results which would be both valuable to science and applicable to clinical practice. The proposal was placed before the Beit Research Fund Committee, the trustees of a fund which had been placed at the disposal of the British Homœopathic Association by Mr. Otto Beit for purposes of scientific research. The necessary support was liberally given by the Association, and still further funds are allotted for continuing the work. The absorption spectra of blood have engaged the attention of many able and distinguished workers, but the investigation has usually had reference to the visible spectra of hæmoglobin and other colourings and to derivatives of these. The work now to be described has for its object the investigation of the absorption spectra of blood sera in the ultra-violet region. The serum is freed as much as possible from corpuscles by the centrifuge, and the clear pale yellow liquid itself is studied with a view to determining the various characteristics of the absorption bands and to finding how these may be accounted for.

scholarly journals The ultra-violet absorption spectra of certain aromatic amino-acids, and of the serum proteins

1929 ◽  
Vol 104 (730) ◽  
pp. 198-205 ◽  
Keyword(s):  
Amino Acids ◽  
Absorption Spectrum ◽  
Absorption Spectra ◽  
Serum Proteins ◽  
Aromatic Amino Acids ◽  
Ultra Violet ◽  
Protein Molecule ◽  
Absorption Bands ◽  
Extinction Coefficients ◽  
Phenyl Alanine

The absorption spectra of the aromatic amino-acids and of the serum proteins have been investigated by Dhéré, 1909 (1), who obtained values for the wave-lengths in close accordance with those found by subsequent workers; he was unable to measure the extinction coefficients, sine at the time no suitable apparatus had been devised. He further noted that the absorption spectrum of tyrosine moved towards the red and tryptophane were responsible for the absorption spectrum of protein. In 1916, Kober (2) investigated the absorption bands of the aromatic amino-acids. Ward (3) in 1923, and Marchlewski (4) in 1925, made use of the rotating sector to measure the extinction coefficients of tyrosine, tryptophane, and phenyl-alanine. The absorption spectrum of tryptophane has also been measured by Abderhalden and Hass (5). In 1922, Judd Lewis (6) measured the absorption spectra of the serum proteins. Stenström and Reinhard (7) have confirmed the work of Dhéré, showing that the aromatic amino-acids present in the protein molecule were responsible for its absorption spectrum.

Mechanism of anionic coordination dimerization of isoprene

1981 ◽  
Vol 46 (7) ◽  
pp. 1600-1606 ◽  
Author(s):  
Jan Bartoň ◽  
Karel Volka ◽  
Miroslav Kašpar ◽  
Vlastimil Růžička
Keyword(s):  
Gas Chromatography ◽  
Alkali Metal ◽  
Absorption Spectra ◽  
Visible Radiation ◽  
Absorption Bands ◽  
Absorption Spectrophotometry ◽  
Spectrophotometric Data ◽  
Oligomeric Forms

The mechanism of controlled anionic coordination dimerization of isoprene (i.e. 2-methyl-1,3-butadiene) in the system tetrahydrofuran-isoprene-alkali metal-dialkylamine was investigated by using absorption spectrophotometry in the range of visible radiation and gas chromatography. The effect of the alkali metal (Li, Na, K) and dialkylamine (dicyclohexylamine, N-isopropylcyclohexylamine, N-methylisopropylamine) on the absorption spectra was tested. By comparing chromatographic and spectrophotometric data, the absorption bands in the range of visible radiation were identified with the existence of π-complexes between oligomeric forms of isoprene and alkali metal dialkylamide.

scholarly journals Unraveling the electrochemical and spectroscopic properties of neutral and negatively charged perylene tetraethylesters

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Christian Wiebeler ◽  
Joachim Vollbrecht ◽  
Adam Neuba ◽  
Heinz-Siegfried Kitzerow ◽  
Stefan Schumacher
Keyword(s):  
Absorption Spectra ◽  
Density Functional ◽  
Energy Levels ◽  
Spectroscopic Properties ◽  
Absorption Bands ◽  
Functional Theory ◽  
Vertical Excitation ◽  
Hartree Fock ◽  
Tauc Plot ◽  
Electrochemical Approach

AbstractA detailed investigation of the energy levels of perylene-3,4,9,10-tetracarboxylic tetraethylester as a representative compound for the whole family of perylene esters was performed. It was revealed via electrochemical measurements that one oxidation and two reductions take place. The bandgaps determined via the electrochemical approach are in good agreement with the optical bandgap obtained from the absorption spectra via a Tauc plot. In addition, absorption spectra in dependence of the electrochemical potential were the basis for extensive quantum-chemical calculations of the neutral, monoanionic, and dianionic molecules. For this purpose, calculations based on density functional theory were compared with post-Hartree–Fock methods and the CAM-B3LYP functional proved to be the most reliable choice for the calculation of absorption spectra. Furthermore, spectral features found experimentally could be reproduced with vibronic calculations and allowed to understand their origins. In particular, the two lowest energy absorption bands of the anion are not caused by absorption of two distinct electronic states, which might have been expected from vertical excitation calculations, but both states exhibit a strong vibronic progression resulting in contributions to both bands.

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