Frequencies Of Vibrational Bands Research Articles

Direct Observation of the 4-Methoxyphenylnitrene Intersystem Crossing from S1 to T1 Using Picosecond Kerr-Gated Time-Resolved Resonance Raman Spectroscopy

A picosecond Kerr-gated time-resolved resonance Raman (ps-KTR(3)) study of the singlet 4-methoxyphenylnitrene intersystem crossing to produce the triplet 4-methoxyphenylnitrene species is reported. The experimental resonance Raman vibrational band frequencies observed for the singlet and triplet 4-methoxylphenylnitrene species in the time-resolved Raman experiments are compared to each other and to predictions from previously published density functional theory calculations. The structure, properties, and chemical reactivity of the singlet and triplet states of the 4-methoxyphenylnitrenes are briefly discussed.

Complexes of Importance to the Absorption of Solar Radiation

Complexes of atmospheric molecules and atoms with water, H2O·X, where X is H2O, N2, O2, Ar, and CO2, are investigated to evaluate their possible role in the absorption of solar energy and consequently in influencing the Earth's climate. The atmospheric abundance and absorption spectra of these complexes are calculated and used in a line-by-line radiative transfer model to assess their contribution. We have used statistical mechanics to calculate equilibrium constants and the harmonically coupled anharmonic oscillator local mode model to calculate fundamental and overtone OH-stretching vibrational band frequencies and intensities. Parameters for these calculations were obtained with the use of ab initio methods. Apart from the water dimer, no OH-stretching bands are significantly frequency shifted compared to those in the water monomer, implying that observation of the vibrational spectra of these hydrates in the atmosphere will be difficult. Of the studied complexes, we find that the O2 and N2 monohydrates are likely to contribute the most to absorption of solar radiation; however, the absolute absorption is highly dependent on the band shape of the vibrational transitions.

Calculated OH-Stretching Vibrational Transitions of the Water−Nitric Acid Complex

We have calculated fundamental and overtone OH-stretching vibrational band frequencies and intensities of the water−nitric acid complex. The calculations use the simple harmonically coupled anharmonic oscillator (HCAO) local-mode model with local-mode parameters obtained from scaled ab initio calculations and ab initio-calculated dipole moment functions. The ab initio calculations were performed at the HF, B3LYP, and QCISD levels of theory predominantly with the 6-311++G(2d,2p) basis set. We have compared our results for the water−nitric acid complex with results for the water dimer and the nitric acid and water molecules. The results show that the water−nitric acid complex is more strongly bound, and the changes in spectroscopic properties compared to the individual molecules are more significant than those for the water dimer. The total OH-stretching intensity of the water−nitric acid complex is significantly higher than the sum of the intensities for the individual molecules in the fundamental and higher overtone regions. The transitions associated with the hydrogen-bonded OH bond show a very large red shift compared to the OH-stretching transitions of the nitric acid molecule. These red-shifted bands provide likely spectral regions for the detection of the water−nitric acid complex in the near-infrared. The effect of the water−nitric acid complex on atmospheric OH radial productions and absorption of solar radiation is discussed.

A Combined Infrared Photodissociation and Theoretical Study of the Interaction of Ethanol with Small Gold Clusters

The infrared photodissociation spectra of Aun(C2H5OH)m (n = 3, 9, 11; m = 1−4) complexes have been recorded in the 9−11 μm region. The ethanol vibrational band frequencies are observed to be invariant with the size of the underlying gold clusters, indicating that local, rather than global, interactions determine the frequency shifts from the gas-phase values. Experimental results are compared with electronic structure calculations for both Au3(C2H5OH) and Au3(CH3OH). From these calculations a model for the binding of the single alcohol to the gold cluster is proposed which qualitatively accounts for many of the experimental observations.

Calculated CH-Stretching Overtone Spectra of Naphthalene, Anthracene and Their Cations

We have calculated fundamental and overtone CH-stretching vibrational band frequencies and intensities of neutral and cationic naphthalene and anthracene, the smallest of the polycyclic aromatic hydrocarbons. The calculations use a simple anharmonic oscillator local mode model with local mode parameters obtained from scaled ab initio calculations and ab initio calculated dipole moment functions. The ab initio calculations were performed at the self-consistent-field Hartree−Fock and the B3LYP hybrid density functional levels of theory with the 6-31G(d) and 6-311+G(d,p) basis sets. The vapor phase overtone spectra of anthracene and both cations have not yet been observed. We find that the cation frequencies are blue shifted and the overtone transitions are of comparable intensities to those in the neutral molecules, contrary to the fundamental transitions which are significantly weaker in the cations. The method presented here can provide an accurate estimate of CH-stretching overtone spectra of neutral and cationic polycyclic aromatic hydrocarbons.

Fluorescence spectra of isolated molecules in neon and argon matrices: assignment of the lowest emitting states

Highly structured fluorescence spectra are reported for molecules isolated in Ne and Ar matrices. Their excitation spectra are very similar to the gas-phase two-photon ionization spectrum of . Most of the bands seen in emission can be attributed to Herzberg - Teller or Jahn - Teller active modes and to combinations of these modes. The intensity distribution of the fluorescence bands is compared with calculated intensities and shows that the emission is of mixed singlet and character in Ne matrices in nearly equal proportions and of mixed singlet and character in Ar matrices, in a proportion of 4 to 1 in favour of the state. The band frequencies show that these three states are degenerate to within our experimental uncertainty and we estimate their gas-phase energy at . The assignment of ground-state vibrational band frequencies are rediscussed in the light of the present results.

Structural Peculiarities and Phase Transitions of MBBA with Different Thermal Pre-History

Abstract The temperature dependencies of widths and frequencies of vibrational bands in MBBA (N-p-methoxybenzylidene p-n-butylaniline) corresponding to intramolecular vibrations (1100 - 1700 cm−1) were investigated in various thermal regimes. Regularities connecting frequencies and shape parameters with structural peculiarities of MBBA in different phases under fast and slow cooling were found. Besides it was obtained additional information about mechanisms of vibrational band formation in molecular spectra.

The development of structural peculiarities of supercooled MBBA in Raman spectra contours

The temperature dependencies of widths and frequencies of vibrational bands corresponding intramolecular vibrations (1100 cm−1 -1700 cm−1) were investigated for supercooled MBBA (N-p-methoxybenzylidene p-n-butylaniline) by Raman spectroscopy. Clearly defined correlation between shape parameter (width), vibrational band position and structural peculiarities MBBA in different phases under fast cooling was established.

Direct Characterization of Tire Materials by Photoacoustical Infrared and Proton Induced X-Ray Emission Spectroscopy

Abstract In an effort to find out if compound composition could help explain the observed differences in “chip/chunk tearing” on worn off-the-road tires from two manufacturers, direct characterizations were made on tread lugs from the two tires. Two nondestructive direct analytical methods were used. They are photoacoustical Fourier transform infrared spectroscopy (PA-FTIR) and proton induced x-ray emission spectroscopy (PIXE). These techniques were also used to examine a variety of rubber compounding ingredients, such as polymers and fillers, and model tire compounds containing different levels of these ingredients. PA-FTIR requires essentially no sample preparation. It was successfully used to determine the polymer structure and to suggest the nonblack filler type in highly loaded carbon-black filled, sulfur-cured compounds and in tire sections. The characterization was based upon structural information derived from vibrational band frequencies. Elemental information was obtained by using direct PIXE spectral analysis of polymers, fillers, and two worn off-the-road tire tread lugs. Again, no sample preparation was needed and quantitative information was obtained on the elements present. Results show that the tire that did not display a tear problem was manufactured with a cushion (tread base) and a tread (cap), both containing silica at the 12–15 phr levels. The tire that had a visible chip/chunk problem was constructed with two layers of a very similar stock, but neither layer contains silica.

IR-Spectroscopy of inorganic fluorides dissolved in liquefied noble gases

Vibrational spectra of solutions in liquefied noble gases at low temperatures gives wide scope for obtaining information concerning molecules being studied. The main aspect of interest with liquefied noble gases is their high inertness and transparency from the vacuum ultraviolet up to the radio-frequency region. Thus with the obvious advantage of the high accuracy of determining main molecular parameters (frequencies of vibrational bands, force constants, isotopic shifts, etc.), the cryogenic solution method can be used for the study of extremely aggressive and unstable chemical compounds, which includes a considerable number of inorganic fluorides. Moreover, the mentioned method can be used to study intermediate molecular systems formed by complex processes and photochemical reactions and to determine the symmetry, stoichiometry and structure of these molecules. The present work summarises the results of the study of IR spectra of MF 6 ( M=S, U, Mo, W), ClF n ( n=3, 5), C R 3 SiF 3 ( R=H, Cl), XeF m ( m=2, 4, 6), CrO 2F 2, PF 3, etc., solutions in liquid Ar, Kr and Xe. Regular contour formation is observed and a number of spectroscopic parameters are determined. The structural peculiarities of the studied molecules in liquid noble gases are discussed.

Raman spectra of the rare earth trimetaphosphates

AbstractRaman spectra of anhydrous crystalline powders of all the lanthanide trimetaphosphates (with the exception of Pm(PO3)3) and of yttrium trimetaphosphate have been obtained. These data have been interpreted in a systematic manner based on the known structures of these compounds. Variations of the vibrational band frequencies with atomic number are much less than with the orthophosphates.

Potential dependence of vibrational frequencies of adsorbates on a silver electrode

The frequencies of several vibrational bands of pyridine, pyrazine, p-nitroso dimethylaniline and cyanide adsorbed on a silver electrode have been investigated as a function of the electrode potential using in situ Raman spectroscopy. The frequencies of all the bands investigated were found to decrease linearly with cathodic potential. This observation is independent of the adsorbate and the anions of the supporting electrolyte. Several models explaining this effect are discussed.

Potential dependence of vibrational frequencies of adsorbates on a silver electrode

The frequencies of several vibrational bands of pyridine, pyrazine, p-nitroso dimethylaniline and cyanide adsorbed on a silver electrode have been investigated as a function of the electrode potential using in situ Raman spectroscopy. The frequencies of all the bands investigated were found to decrease linearly with cathodic potential. This observation is independent of the adsorbate and the anions of the supporting electrolyte. Several models explaining this effect are discussed.

Calculation of ionic conductivity activation energies in ionic oxide glasses from spectroscopic data

Activation energies for ionic conduction in inorganic oxide glasses are related to cation-motion vibrational band frequencies from the far infrared spectra of the glasses, and the calculated and observed values are compared.