Showing papers on "Infrared spectroscopy published in 1985"

Polycyclic aromatic hydrocarbons and the unidentified infrared emission bands - Auto exhaust along the Milky Way

Abstract: The unidentified infrared emission features (UIR bands) are attributed to a collection of partially hydrogenated, positively charged polycyclic aromatic hydrocarbons (PAHs). This assignment is based on a spectroscopic analysis of the UIR bands. Comparison of the observed interstellar 6.2 and 7.7-micron bands with the laboratory measured Raman spectrum of a collection of carbon-based particulates (auto exhaust) shows a very good agreement, supporting this identification. The infrared emission is due to relaxation from highly vibrationally and electronically excited states. The excitation is probably caused by UV photon absorption. The infrared fluorescence of one particular, highly vibrationally excited PAH (chrysene) is modeled. In this analysis the species is treated as a molecule rather than bulk material and the non-thermodynamic equilibrium nature of the emission is fully taken into account. From a comparison of the observed ratio of the 3.3 to 11.3-micron UIR bands with the model calculations, the average number of carbon atoms per molecule is estimated to be about 20. The abundance of interstellar PAHs is calculated to be about 2 x 10 to the -7th with respect to hydrogen.

Excimer laser etching of polyimide

Abstract: It is reported that thin films of polyimide are efficiently etched in air at pulsed excimer laser wavelengths of 248, 308, and 351 nm. Etch rate versus incident fluence data are found to obey a Beer–Lambert etching relation. Sharp laser fluence thresholds for significant etching are found to correlate with the wavelength‐dependent absorption coefficient. The absorbed energy density required to initiate significant etching is found, within experimental error, to be independent of the wavelengths examined. It is felt that this information demonstrates the predominantly thermal nature of the laser etching mechanism. Additionally, infrared spectroscopy and coupled gas chromatography/mass spectroscopy were used to identify several gases evolved during pulsed laser etching of polyimide in both air and vacuum.

Evaluation of infrared spectroscopic techniques for analysing chitosan

Abstract: The use of the 3450 cm−1 absorption band as an internal standard in the determination of the extent of N-acetylation of chitosan from the absorbance of the amide I band at 1655 cm−1 was studied. The results show that the technique gives consistent results that are relatively unaffected by whether the sample is air-dried or oven-dried. A number of chitosan samples, covering the range of N-acetyl values from 14% to 72% were analysed by three techniques: infrared spectroscopy using the ratio A1655/A3450, hydrobromide salt titration and residual salicylaldehyde determination. There is a very good correlation between the results from infrared spectroscopy and those from the other two analytical techniques, confirming the validity of the former technique.

Phenomena Induced by Intermolecular Interactions

Abstract: Section 1: Compressed Gases and the Effect of Density.- A. Far Infrared and Infrared Absorption.- Classical Multipole Models: Comparison with Ab Initio and Experimental Results.- Ab Initio Calculations of Collision Induced Dipole Moments.- A Comparative Study of the Dielectric, Refractive and Kerr Virial Coefficients.- The Infrared and Raman Line Shapes of Pairs of Interacting Molecules.- Collision-Induced Absorption in the Microwave Region.- Collision-Induced Absorption in N2 at Various Temperatures.- Far Infrared Absorption Spectra in Gaseous Methane from 138 to 296 K.- Induced Vibrational Absorption in the Hydrogens.- Simultaneous Transitions in Compressed Gas Mixtures.- Molecular Motions in Dense Fluids from Induced Rotational Spectra.- Intercollisional Interference - Theory and Experiment.- Workshop Report: Infrared Absorption in Compressed Gases.- B. Light Scattering.- Ab Initio and Approximate Calcuations of Collision-Induced Polarizabilities.- Depolarization Ratio of Light Scattered by a Gas of Isotropic Molecules.- Depolarized Interaction Induced Light Scattering Experiments in Argon, Krypton, Xenon.- Interaction Induced Rotational Light Scattering in Molecular Gases.- Workshop Report: Light Scattering in Compressed Gases.- Section 2: Liquids and Liquid State Interactions.- A. Atomic Systems.- Theory of Collision-Induced Light Scattering and Absorption in Dense Rare Gas Fluids.- Calculation of Spectral Moments for Induced Absorption in Liquids.- B. Molecular Systems.- Interaction-Induced Vibrational Spectra in Liquids.- Far Infrared Induced Absorption in Highly Compressed Atomic and Molecular Systems.- Theoretical Interpretation of the Far Infrared Absorption Spectrum in Molecular Liquids: Nitrogen.- Molecular Dynamics Studies of Interaction Induced Absorption and Light Scattering in Diatomic Systems.- Interaction Induced Light Scattering from Tetrahedral Molecules.- Local Fields in Liquids.- Pressure - An Essential Experimental Variable in Spectroscopic Studies of Liquids.- Workshop Report: Liquids and Liquid State Interactions.- Section 3: Solid State, Amorphous, and Ionic Systems.- Study of the Collective Excitations in H2 as Observed in Far Infrared Absorption.- Induced Light Scattering in Disordered Solids.- Infrared Induced Absorption of Nitrogen and Methane Adsorbed in NaA Synthetic Zeolite.- Charge Induced Effects in Solid Tritium and Deuterium.- Workshop Reports: Some Considerations on Spectra Induced by Intermolecular Interactions in Molecular Solids and Amorphous Systems.- Section 4: Induced Transitions in Allowed Spectra.- Collision-Induced Effects in Allowed Infrared and Raman Spectra of Molecular Fluids.- Raman Scattering from Linear Molecules.- The Interference of Molecular and Interaction-Induced Effects in Liquids.- Interaction Induced Spectra of "Large" Molecules in Liquids.- The Infrared Spectrum of HD.- Workshop Report: The Interference of Induced and Allowed Molecular Moments in Liquids.- Section 5: Related Subjects.- Contribution of Bound Dimers, (N2)2, to the Interaction Induced Infrared Spectrum of Nitrogen.- Vibrational Spectral Lineshapes of Charge Transfer Complexes.- Collision-Induced Effects in Planetary Atmospheres.- Time-Domain Separation of Collision Induced and Allowed Raman Spectra.- Collision-Induced Radiative Transitions at Optical Frequencies.- Comments on Hyper-Rayleigh Scattering.- Comments on the Spectra of the Halogens and Halogen Complexes in Solution.- Author index.- Chemical index.

IR characteristics of hydrotalcite-like compounds

Abstract: The infrared spectra of well characterized hydrotalcite-like compounds with M2+/M3+= 2/1 and M2+/M3+=3/1 chemical ratios indicate that octahedral cation ordering is only present for the 2/1 composition. For M2+/M3+ ratios greater than 2/1, the octahedral sheets are disordered although local cation order can be present through cation segregation. The order-disorder characteristics of these compounds can be explained by the total cation charge around any hydroxyl which cannot exceed seven units nor be lower than six. In addition, the infrared spectra suggest that the interlayer anions are symmetrically perturbed, the electrostatic interaction being greater for the 2/1 compositions.

Structure of rhodium in an ultradispersed Rh/Al2O3 catalyst as studied by EXAFS and other techniques

Abstract: The structure of rhodium in an ultradispersed 0.57 wt % Rh/y-Al,O, catalyst before and after CO adsorption was studied with extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), temperature programmed reduction (TPR), CO infrared spectroscopy, and H2 and CO chemisorption. With the aid of these complementary techniques, it could be established that the structure of the rhodium catalyst was completely different before and after CO adsorption. Before CO adsorption and after reduction of the catalyst at 593 K, all the rhodium was reduced and in the form of three-dimensional metallic crystallites. CO adsorption disrupted the metal-metal bonds in the crystallites, leading to isolated rhodium geminal dicarbonyl species in which the rhodium was present as Rh'. Each rhodium ion was surrounded by two carbon monoxide molecules and three oxygen anions of the support.

The infrared predissociation spectra of water clusters

Abstract: Infrared predissociation spectra of water clusters have been measured in the frequency range 3000–3800 cm−1 using a molecular beam–color center laser apparatus. The transition from a spectrum resembling that of liquid water to that of the dimer is clearly seen. Detailed theoretical analyses using normal mode theory, local mode theory, and a quantum simulation method are used to interpret the spectrum in terms of a potential surface that includes both intramolecular and intermolecular degrees of freedom.

Infrared determination of the degree of substitution of hydroxyl by carbonate ions in human dental enamel

Abstract: About 11 +/- 1% of the carbonate ions in a human tooth enamel specimen (dense fraction, sp. g. greater than 2.95) were found to be in the A-sites, replacing hydroxyl ions. The determination was made with a difference infrared spectrometry technique utilizing both tooth enamel and a reconstituted biological apatite with a known amount of replacement of hydroxyl by carbonate ions.

IR Studies of NH3, Pyridine, CO, and NO Adsorbed on Transition Metal Oxides

Abstract: Chemisorption of small molecules is often used as a probe for By probing the surface properties of transition metal oxides the interaction of molecules with the surface, information is often obtained on the oxidation state, the coordination symmetry, the degree of coordination unsaturation of the surface cations, the acid-base properties of the surface hydroxyl groups, and the presence and the nature of surface Lewis acid and B rosnsted acid sites This information is deduced from experimental measurements of the adsorption isotherms, the heats of adsorption, the thermal desorption spectra, and the vibrational spectra of the adsorbate Until recently, when high resolution electron energy loss spectroscopy became available, vibrational spectra were obtained with infrared spectroscopy Laser Raman spectroscopy has seldom been used because of the low Raman scattering cross section of most molecules

Hydrogen localization near boron in silicon

Abstract: Several models of boron neutralized by atomic hydrogen in silicon were tested by secondary ion mass spectrometry and infrared spectrometry. The hydrogen concentration is comparable to that of boron. Boron neutralization appears as a drop in free‐carrier absorption and as an increase in resistivity. A new infrared vibrational mode attributed to 〈111〉 vibrations of H tied to Si appears at 1875 cm−1.

Order–disorder transitions in Langmuir–Blodgett monolayers. I. Studies of two‐dimensional melting by infrared spectroscopy

Abstract: A two step melting process in Langmuir–Blodgett (LB) monolayer assemblies of cadmium arachidate (CdA) has been studied by infrared spectroscopy in conjunction with thermal measurements. These techniques have allowed, for the first time, the investigation of detailed structural changes which occur during heating, melting, and annealing cycles. Prior to the melting point, a pretransitional disordering of the hydrocarbon tails was observed. This was followed by a catastrophic breakup of the cadmium lattice at a temperature corresponding to the melting point as measured by differential scanning calorimetry (DSC).

On the mechanism of specific phosphate adsorption by hydroxylated mineral surfaces: A review

Abstract: The mechanism of specific phosphate adsorption by hydroxy‐lated mineral surfaces comprises two aspects: the phosphate‐hydroxyl surface reaction and the configuration of the adsorbed phosphate ion. Evidence pointing to ligand exchange as the mechanism of the phosphate‐surface hydroxyl reaction include kinetics of adsorption and desorption; hydroxyl ion release; infrared spectroscopy, and stereochemical calculations. Data pertaining to the coordination of adsorbed phosphate on hydroxy‐lated mineral surfaces have not been conclusive overall. Isotopic exchange experiments and studies of desorption kinetics do not provide definitive information on surface coordination. Measurements of hydroxyl ion release and crystallographic calculations provide support for the existence of both monodentate and bidentate surface complexes of phosphate ions. Infrared spectroscopic investigations suggest a binuclear complex on dried, phosphated goethite. However, these studies cannot be extrapolated automatically to so...

Brownian motion and vibrational phase relaxation at surfaces: CO on Ni(111).

Abstract: The temperature dependence of the internal stretch vibrational mode of CO chemisorbed on Ni(111) has been studied with the use of infrared spectroscopy. The width of the absorption peak of the bridge-bonded molecules exhibits a strong temperature dependence. A theory is developed which accounts well for the experimental results. It shows that the peak broadening is caused by anharmonic coupling to one particular low-frequency mode, namely a hindered rotation.

Infrared spectroscopy at the surface of clusters: SF6 on Ar

Abstract: We have succeeded in obtaining infrared spectra of molecules adsorbed on the surface of clusters. The method is based on the photodissociation spectroscopy technique developed in our laboratory for the study of cluster beams and on a simple but effective way to prepare mixed clusters in which an IR chromophore is attached to the surface of a nonabsorbing host cluster. The possible extension of this technique to the study of molecular spectroscopy at the surface of clusters large enough to simulate crystal and liquid surfaces is also discussed.

The vibrational predissociation spectroscopy of hydrogen cluster ions

Abstract: Although molecular ion spectroscopy has progressed rapidly[1], there has been very little spectroscopy done of weakly bound ionic clusters[2,3]. These clusters play an important role in atmospheric chemistry and have been studied extensively in thereto-chemical and kinetic experiments over the past decade[4]. Much of our understanding of the dynamics and structure of cluster ions to date has relied on the results of ab initio quantum calculations. Stimulated by the theoretical work, we have begun experiments on the infrared spectroscopy of cluster ions, and have recently made the first spectroscopic observation of the protonated hydrogen clusters H n + (n=5,7,9,11,13 and 15).

Ionized polycyclic aromatic hydrocarbons and the diffuse interstellar bands

Abstract: A good case has recently been made that the unidentified infrared emission features arise from positively charged, partially hydrogenated polycyclic aromatic hydrocarbons (PAHs). In this letter it is suggested that these exceedingly stable ions are also the carriers of the diffuse interstellar bands. Although a large variety of PAH isomers is possible, the more condensed forms are substantially more stable than the less condensed forms and are expected to be dominant in the harsh interstellar environment. While neutral PAHs do not absorb in the visible, their ionized counterparts do. Because of their low ionization potential, a substantial fraction of the interstellar PAHs will be ionized. Visible spectra of the most stable PAH cations isolated in glasses are compared directly to the interstellar band spectra. Although the laboratory spectra are on an extremely compressed scale and solid state shifts are present, the comparison is favorable. Since little information is available concerning the spectroscopic properties of these species in the gas phase, a considerable amount of laboratory and theoretical work is called for to test this hypothesis.

Microwave and infrared characterization of several weakly bound NH3 complexesa)

Abstract: We present the results of microwave and infrared spectroscopic studies of several van der Waals complexes of NH3. These results were obtained with a molecular beam electric resonance spectrometer. The microwave spectroscopy of the complexes (NH3)2 and Ar–NH3 show that both systems are nonrigid. The observed dipole moments for (NH3)2[0.74(2) D] and (ND3)2[0.57(1) D] are not compatible with the presently accepted theoretical structure. Ar–NH3, which has a complicated and currently unassigned microwave spectrum, exhibits Q branch inversion transitions near 19 GHz which indicate that the NH3 subunit is likely to be a near‐free rotor. Infrared studies of the complexes NH3–HCCH, NH3–CO2, (NH3)2, Ar–NH3, NH3–OCS, NH3–N2O, and NH3–HCN have been carried out with a line tunable CO2 laser. Only for NH3–HCN were no infrared resonances discovered. Photodissociative transitions are observed in all of the other systems. Band origins for the photodissociative infrared transitions involving the ν2 umbrella motion of NH3 were determined for NH3–HCCH [984.4(9) cm−1], NH3–CO2 [987.1(2) cm−1]. NH3–OCS [981.5(15) cm−1], and NH3–N2O [980(2) cm−1]. The observation of an infrared transition for Ar–NH3 at 938.69 cm−1, which is 40 cm−1 lower than the band origins in the other NH3 complexes, lends support to the model of Ar–NH3 mentioned above. NH3–HCCH, NH3–CO2, (NH3)2, and Ar–NH3 were studied in microwave‐infrared double resonance experiments in order to eliminate much of the inhomogeneous broadening present in their infrared spectra and to aid in the rotational assignment of the infrared spectra. Linewidths were determined for NH3–HCCH (0.15 GHz) and for NH3–CO2 [14(6) GHz]. An important result of this study is that the dissociation energies of all the complexes studied, except for NH3–HCN, are established to be less than 990 cm−1, i.e., 2.8 kcal/mol.

Protein Conformation by Infrared Spectroscopy: Resolution Enhancement by Fourier Self-Deconvolution

Abstract: Fourier self-deconvolution (FSD) has been employed to enhance the resolution of the infrared spectra of proteins in the solid state and in D2O solution. The feasibility of using diffuse reflectance spectrometry for measuring the infrared spectra of solid proteins has been demonstrated. FSD permits inherently broad absorption bands to be resolved into distinct peaks which can be associated with specific protein secondary structures. Because the areas of the resolved peaks are the same as the areas of the previously unidentifiable components, this new method should enable quantitative estimates of the proportion of each conformation in a protein to be calculated.

Amide I band of IR spectrum and structure of collagen and related polypeptides

Abstract: The infrared amide I band of collagens (rat and cod skin) and related compounds (polyproline, polyglycine, and polytripeptides) was studied. Assignment of amide I-band components for polyproline II and polytripeptides (Gly-Pro-Pro)n and (Gly-Pro-Gly)n in the solid state and water solution was made. Three amide I components observed in the polypeptide spectra were attributed to three different peptide CO groups in each triplet. On the basis of this assignment, the interpretation of the amide I multicomponent structure in collagen and isomorphous oligo- and polypeptides was attempted. The ordering of intra- and intermolecular hydrogen bonds involving peptide CO groups in collagen and related compounds was discussed.

High-resolution far-infrared (20–350-cm −1 ) spectra of several isotopic species of H 2 O

Abstract: Far-infrared pure rotational spectra of H216O, H218O, HD16O, HD18O, D216O, and D218O have been measured with a high-resolution Fourier-transform spectrometer with an apparatus function of 0.004 cm−1 in the region from 20 to 350 cm−1. Altogether about 1200 lines have been assigned and measured with an accuracy that is believed to be ~0.0002 cm−1 (~6 MHz), so that many of the frequencies should be of use in the calibration of far-infrared spectrometers.

Microcalorimetric and Fourier transform infrared spectroscopic studies of methanol adsorption on alumina

Abstract: Adsorption microcalorimetry and infrared measurements using CH/sub 3/OH, CD/sub 3/OH, and CHD/sub 2/OH show the existence of at least three steps during the adsorption of methanol on alumina activated at 773 K. At very low coverages, molecules coordinated on the strongest Lewis sites are evident, which easily transform into bridged methoxide species. With increasing coverage, another form, irreversibly adsorbed at room temperature but desorbed by evacuation at 373-473 K, becomes predominant. It is identified as undissociated methanol strongly hydrogen bonded on a cation-anion couple having a strong basic character. Finally, at high coverages a reversible form hydrogen bonded to basic sites is detected. 33 references, 7 figures, 1 table.

Vibrational phase relaxation at surfaces: CO on Ni(111).

Abstract: The temperature dependence of the internal stretch vibrational mode of CO adsorbed on Ni(111) has been studied by infrared spectroscopy. The results are successfully analyzed by a model for vibrational phase relaxation. It is found that anharmonic coupling between the C-O stretch mode and a low-frequency frustrated rotation gives the dominant contribution.

Structure and dynamics of the excited CH–chromophore in (CF3)3CH

Abstract: The absorption spectra of gaseous (CF3) 3CH (1,1,1,3,3,3‐hexafluoro, 2‐trifluoromethyl propane) were recorded in the IR between 800 and 12 000 cm−1 by high resolution interferometric Fourier transform techniques and in the visible from 12 000 to 17 000 cm−1 by laser photoacoustic spectroscopy. Instead of single bands in the CH overtone region, complex multiplet structures were observed. Thirty‐nine bands were assigned as arising from the interacting CH‐stretching and CH‐bending manifolds, which account for most of the absorption in the overtone region. The results can be understood quantitatively with an effective, tridiagonal many‐level Fermi resonance Hamiltonian. Close agreement is obtained for the positions and intensities of the observed spectral features using only seven spectroscopic parameters. The experimental and theoretical results are summarized in Tables II, III, and IV. The Hamiltonian can be used to calculate and understand the time‐dependent redistribution of vibrational energy between the...

Crystalline Quartz as an Internal Pressure Calibrant for High-Pressure Infrared Spectroscopy

Abstract: Raman spectra of aqueous phospholipid bilayers and aqueous micellar solution of surfactants at high pressure have been studied in this laboratory. However, some normal modes in these systems are Raman inactive or weakly active, and most of the normal modes of the methylene chains in these systems are highly dispersed. In order to further understand the pressure effects on the vibrational dynamics in these systems, we have extended our pressure studies to the Fourier transform infrared spectra of these aqueous systems, using a diamond anvil cell.