Resonance raman spectra of würster's cation dimers: p-phenylenediamine and 2,3,5,6-tetramethyl-p-phenylenediamine

Resonance Raman spectra have been observed for the dimers of p-phenylenediamine cation (PPD⁺) and of 2,3,5,6-tetramethyl-p-phenylenediamine cation (TMPD⁺). When the exciting light frequency approached the absorption bands characteristic of the dimers, new polarized Raman lines appeared at 161 cm^?1 for (PPD⁺)₂ and at 117 cm^?1 for (TMPD⁺)₂ with a striking resonance enhancement. The resonant behaviour as well as the frequency values indicate that they are reasonably assigned to the interradical stretching vibrations of the parallel D_2h dimer molecules.     

Resonance raman spectra and excitation profiles of soret-excited metalloporphyrins

Resonance Raman spectra of nickel, chromium, and copper porphyrins, excited at their Soret maxima, show decreasing scattering intensity due to depolarized modes. This order correlates with diminished ¹Q(0-0) absorption in the porphyrins. The data are interpreted in terms of Jahn-Teller distortions in both Q and B states. General agreement between predicted and observed excitation profiles of nickel etioporphyrin I support a vibronic treatment of the excited states. The effect of tight focusing of the incident beam is to quench most Raman scattering intensity, except the 1384 cm^?1 line of the nickel complex.     

Resonance raman spectra and quantum yields of MoS42−

Resonance Raman scattering of MoS₄^2? was studied in aqueous solution by irradiating its strong 4700 Å absorption band with five different lines of an Ar⁺ laser. The vibrational structure of the resonance spectra is discussed. Cross sections and quantum yields for the total scattered radiation were determined using NO₃^? as an internal standard.     

Resonance raman and infrared spectra of ClO3 radicals in electron irradiated NaClO3

Resonance Raman and infrared absorption spectra of ClO₃ radicals have been observed from measurements of crystalline NaClO₃ irradiated at 77 K with 1.5 MeV electrons. The ClO₃ radicals occupy two sets of nonequivalent sites; radicals at one site are observed from resonance scattering using 6328 Å excitation while those at the other site are observed from resonance scattering with 5145 Å excitation. The red sensitive radicals decompose at 77 K with a half-life of ≈29 min while the green sensitive radicals are more stable at this temperature.     

Surface-enhanced raman spectra of dyes and organic acids in silver solutions: chloride ion effect

We have recorded surface-enhanced Raman (SER) spectra of two different classes of compounds, cationic dyes and organic acids, and studied their chloride ion effects on the surface-enhanced Raman scattering (SERS) activities of the silver solution. For the positive charge dyes, rhodamine 6G (R6G) and 1,1'-dimethyl-2,2'-cyanine iodide (DECI), no SERS could be observed without the addition of chloride ions because of lack of the electrostatic interaction between the dye species and the silver particles in the silver solution. The chloride ions served to enlarge silver particles and to contribute the existence of the surface active sites, making the silver solution SERS active to the dye samples. Surface-enhanced resonance Raman scattering (SERRS) intensity of the dye molecules increased with the chloride ion concentration. After reaching a maximum intensity, a Cl- quenching effect on the intensity took place. For the organic acids, benzoic acid and p-aminobenzoic acid (PABA), SERS could be observed without the coexistence of chloride ions. The intensity of the Raman scattering did not vary significantly in the presence of small amount of chloride ion. At high Cl- concentration, quenching SERS intensity began to take effect.     

Electronic spectra and structure of some phenoxazone-type dyes

Quantum-mechanical calculations of the electronic structure and spectra of a number of phenoxazone dyes are given. The distribution analysis of pi-electron density in the ground and excited states makes clear the origin of the colour of these compounds and gives the possibility of direct assessment of organic reagents in terms of colour contrast and sensitivity of analytical reactions. This is illustrated for a series of dihydroxy derivatives of phenoxazone dyes.     

Photoelectron spectra of p-terphenyl in gaseous and solid states

The high resolution photoelectron spectrum of gaseous p-terphenyl and the spectral response of its photoemission in solid state were measured. Both spectra - gaseous and solid - were in good agreement when a slight shift was assumed. The first vertical ionization potential in the gas phase was 8.20 eV and the potential obtained from the threshold value of the photoemission of crystalline p-terphenyl was 6.1 eV. The conformations in both phases were also discussed.     

Vibrational spectra of certain triphenylmethane dyes and their structure in solution

A combined analysis of two types of vibrational spectra (Raman and infrared) has proven the lactone structure of colorless solid preparations of phenolphthalein and thymolphthalein. It has been shown that phenolsulfophthalein, its alkyl derivatives, and bromcresol purple exist in the solid state primarily in the form of an intensely colored zwitterion; bromphenol blue and bromthymol blue exist primarily in the form of a colorless sultone. For the ionized forms of triphenylmethane dyes (cationic and anionic chromophore systems) vibrations with a frequency near 1360 cm^–1 are characteristic in the IR spectra and also in the Raman spectra.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 6, pp. 688–698, November–December, 1990.     

Electronic spectra and π-electronic structure of some hydroxyazo dyes

The electronic spectra of some hydroxyazo dyes, derivatives of azobenzene and benzeneazonaphthalene, are investigated and electronic transitions in the UV and visible regions assigned.The difference in spectral assignment of o- and p-hydroxyazobenzenes is explained using MO theory.Observations are made about possible azo—quinonehydrazone tautomerism in o-,m- and p-hydroxy derivatives of 4-phenylazo-1-naphthol and 1-phenylazo-2-naphthol and the quantitative value for the contribution of each tautomeric form is calculated.Calculations using the SCl—Cl method, within the PPP approximation, are performed for some hydroxyazo derivatives. The results of the calculations agreed significantly with the experimental spectral curves. Spectral differences between o- and p-hydroxyazobenzenes are established. It is shown that there is charge transfer from the aromatic rings to the azo group in the first excited singlet state.     

Resonance raman spectra of meso-tetramethylporphine,meso-tetraethylporphine and their nickel complexes measured by using the sers technique

Surface-enhanced resonance Raman scattering spectroscopy was applied to measure the vibrational spectra of meso-tetramethylporphine (TMP), meso-tetraethylporphine (TEP), and their nickel complexes in layered structures having CaF₂/sample/Ag (structure I) and CaF₂/Ag/sample (structure II) configurations. The surface spectra clearly prove that, when the samples come into contact with Ag atoms (structure I) or a vacuum-deposited Ag film (structure II), they undergo chemical processes such as metal-incorporation and metal-exchange reactions, and a structural change.     

Infrared and polarized raman spectra of kainite

The i.r. and Raman spectra of KMgClSO₄·3H₂O and its deuterated compound KMgClSO₄·3D₂O have been recorded and analysed. Due to site symmetry effects the i.r. inactive modes appear as sharp bands in the i.r. spectrum. Water bands indicate strong hydrogen bonding and show the presence of three crystallographically distinct water molecules in the unit cell.     

Stark effects on the phosphorescence spectra of p-benzoquinone

Stark effects on the phosphorescence spectra of p-benzoquinone have been studied in naphthalene crystals at temperatures between 1.7 and 30 K. The experimental data establish that the band splitting of 24 cm^?1 arises from a double minimum potential in the T₁ state.     

Resonance raman effect of solid copper thiophosphate

The resonance Raman spectra of solid Cu₃PS₄ excited by seven lines of Ar⁺ and Kr⁺ lasers are reported. The excitation profiles of the Raman fundamentals and the first overtone of the totally symmetric vibration were obtained from the corrected intensity measurements. For some of these vibrations the maxima of the excitation profiles fell near the visible absorption peak. The anharmonicity constant for the totally symmetric mode is also computed.     

Molecular vibrations,electronic structure and conformation of diprotonated thiocarbohydrazide

The infrared spectra of diprotonated species of thiocarbohydrazide and its perdeuterated derivative have been examined in the crystalline state. A complete vibrational assignment with a full normal coordinate treatment based on a Urey—Bradley type intramolecular potential Function supplemented with a valence force function for the out of plane and torsional modes is proposed and the origin of the amide II band splittings is explained. A CNDO/2 study of diprotonated thiocarbohydrazide and its neutral molecule is undertaken and the changes in the molecular electronic structures and conformations consequent to protonation are determined and briefly discussed. The magnitude of the N—N⁺H₃ torsional barrier is estimated to be 21 kJ mol^? (5.0 kcal mol^?1) whereas the barrier for the C—N group is found to be 92 kJ mol^?1 (22.0 kcal mol^?1).     

Infrared and raman spectra of crystalline nitric oxide

Infrared and Raman spectra of polycrystalline samples of nitric oxide N₂O₂, at temperatures between 18 and 80 K have been recorded, and several new low frequency peaks observed. The Raman spectrum of the liquid at 115 K has also been obtained, in an attempt to distinguish between vibrations characteristics of the dimerized molecule and of the lattice. The observed features are discussed in terms of the known molecular and crystal structures.     

Syntheses and raman spectra of nitrosyl fluorometallate salts

Nitrosyl salts containing MF^-₆, MF⁼₆, MF^≡₆, MF^-₇ and MF⁼₈ (M = Cr, Mo, W, Re, Rh, Ru, Os, Ir, Pd, Pt, and Ru) have been synthesized using NOF + F₂ or NO with the appropriate metal or metal fluoride as reactants. All of the compounds were characterized by their Raman spectra and each spectrum was analysed in terms of the fundamental vibrations of cations and anions. Analysis of the Raman spectra of the product formed in the reaction of NOAuF₆ with NOF and F₂ lead to the conclusion that (NO)₂Au(IV)F₆ is a reaction product.